Re-Training with R+
When we first start making the switch over from traditional training, to a positive reinforcement focused training approach, we have to remember that most previously trained behaviors with R- will naturally fall apart when we stop using R-. We can rebuild them with R+ but to be able to do so requires learning a whole new set of skills for both human and horse; which takes a lot of time and patience.
This makes it very hard, and sometimes completely impossible, to just "switch to R+" while expecting to be able to keep doing what you've always been doing... You are absolutely going to have to re-train all the same "normal" behaviors at one point or another if you wish to wean out using R- and P+ in your training. All those behaviors we take for granted in our more experienced and "trained" horses... like leading, backing up, turning when they feel the lead rope, following us, picking their head up from the grass, not dragging you to the grass, being ridden.... will either have to be maintained in whatever way they were originally trained, or re-taught.
In some cases... I do recommend to students maintaining certain behaviors with the original training while starting to integrate in positive reinforcement to strengthen the behavior, and possibly "counter condition" it (to make the behavior less aversive or improve the response from the horse), BUT! this is a very case by case situation and very much depends on variety of factors. Some horses with some behaviors respond exceptionally well to this, and some absolutely do not.
Quite a few of my horses have many R- trained behaviors that they appear to respond very well to, so I kept them "as is" and maintained the R- OR I kept them "as is" and added positive reinforcement.. gradually over time fading out the use of R- and letting them naturally become "R+ behaviors" as much as possible (though I can never guarantee they are completely R+ because they have an R- background - but that's okay with me.. as long as my horses are okay with it, and they appear to be). And... then there are some horses with some behaviors where I thought this "combining" might be a good idea and unfortunately it backfired completely. I lost a lot of progress in the training, poisoned cues, and created a bit of a mess. So, be careful. If you can take the time to re-train a behavior from the start with R+, please do! It's a much safer route in the long run.
So, with that being said.... What happens when you have a horse that is previously fairly well "trained" with R- , but now you want to switch over to as much R+ as possible? You have a horse that has a fairly decent sized repertoire of R- behaviors, like leading and riding, but has minimal R+ experience and a very small repertoire of R+ behaviors. You want to be able to interact with your horse, lead them to and from the barn, ride them, and so on.. but now you realize that to do all those things you have to use R- because your horse doesn't know how to do it any other way, but you have decided you don't really want to do that... so now what?
Here are your options...
Option A: You pretend your horse is suddenly a feral animal that knows zero percent of anything, and you completely start from scratch. You don't assume anything, you don't just "lead your horse from the pasture to the barn because it's feeding time", and you don't even go in the pasture with them until you're sure they are prepared for that step. THIS is how I start working with most horses that come to me for training. Show horses, young horses, old horses.. doesn't matter. They go into a turnout or stall with a run-out, and they stay there until I can lay a good foundation and build a reasonable enough repertoire of behaviors that I can do more with them "hands on". Step by step I rebuild every single thing they know until I can do everything "normal" with them via R+ trained behaviors.
Doing this requires setting up the horse's living arrangements carefully, so that they don't need to be moved and humans don't "have" to go into the space with them. This can seem impractical and even like a much longer road, but I've found it to be the most "thorough" way of going about re-training and you'd be surprised how quickly you get back to "normal".
Option B: Maintain some R- behaviors as R- behaviors, "leave them be" so to speak. Don't combine with positive reinforcement, don't even have your food rewards on you... lead like you've always lead, groom like you've always groomed... whatever it is. If your horse is not in distress or fearful it is an option to leave some behaviors "as is" while you build a repertoire of R+ behaviors to slowly replace the old R- behaviors. One at a time pick behaviors and activities you do together to replace, and focus on those... slowly weeding out the old stuff and replacing it with the new. Usually when doing things this way, I will first build some basic behaviors I teach all horses (like targeting, "manners", etc) and then tackle some problem areas that are critical to address. Example; a horse that's hard to catch out of the pasture. I can re-build this whole interaction between human and horse with R+ and still lead the horse from the pasture back to the barn with R- (though usually I will also recommend some kind of counter conditioning process and assessing the reasons behind why the horse doesn't want to go back to the barn etc).
This process is typically the "easiest" to get people to try, and most "practical" in many situations. It also enables some level of "normality" in the handling of the horse on a daily basis, but you have to be careful to be consistent and be very clear about when you are and are not working with R+ as to not poison cues and create frustration. You can even choose to maintain behaviors used by other R- trained handlers with your horse, to avoid confusion and inconsistency.
In a nutshell, these are the two ways I recommended starting the re-training process in a safe and consistent way. But first.... I'd like to talk some more about why it's so important to be cognizant of when you're using R- and when you're using R+, and making that decision of how to go about re-training.
This is a little long, please forgive me, I feel this is really important.
All behavior has a reason. There is always a reason and motivation behind anything your horse does with you/for you. If a horse's original motivation to perform a behavior was to get relief from pressure, the behavior will fall apart if that pressure ceases to exist. They will no longer be seeking relief, so they will be unmotivated to perform said behavior. To keep that behavior you will either need to maintain the R- or you will have to give the horse a new reason to perform the behavior... through R+. BUT! Re-training behaviors takes time! You and the horse have to take the time it takes to learn the new set of skills, so we can't just one day decide "Horse, you are now R+ trained, please respond accordingly". Unfortunately.... it does NOT work that way (I've tried, lol) and we will end up frustrated and disappointed with our horses and ourselves when the training is seemingly "failing".
If you're going to leave behind your old repertoire, you have to create a new one.. and that takes time and patience and taking a huge leap backwards in your "expectations" of your horse.