Depending on how long you have to train, you may be missing some training volume from the 4 days. I would NOT do days 1-3 one week, then days 4-2 the next week and so on. Rather, I would do the template week by week, adding elements from Day 4 to your other training sessions, if possible.
My above answer is applicable to every template we make, yes.
You could do them in less than 90 minutes for the traditional template, though if you include an extra exercise you’re going to be pushing it. Plenty of ways to cut down training time with rest period adjustment, warming up the next movement while you’re doing the previous one, etc.
Would it be inadvisable for someone with less training age (<1 year) to run the 4 day templates rather than 3, if they like going to the gym more often? Given that they already respond well to 3 day templates.
I think we should evaluate the frequency and the training volume separately. So, while the volume in one of our 4-day templates is likely to be too high for you given that you’re responding well to the 3-day template, the frequency may be fine.
I wouldn’t change anything if it’s working though.
Since 4 day training can be modified to be done in a 3 day split by adding elements to training days do you have any advice which exercises would be good to combine?
For example if one of the training days is more focused on the lower body would you add another lower body exercise or an upper body exercise from the 4th day?
You could do it either way. I think if you’re adding a priority exercise, e.g. one that’s typically programmed first, I’d add it to the end of the opposite focus day’s work. If it’s a 3rd exercise you’re adding, I’d do it on the same body parts’ focused day. If it’s a second exercise, I don’t have a strong preference.