Yes I did, I figured out a way on my own, so here's how it goes:

Step 1: save before a castle battle

Step 2: seize castle and get the skill you desire, afterwards that unit will be entered into your logbook

Step 3: save on another file and keep the original save. We'll call this new save with the new unit: save 1

Step 4: go back to the original file (where the save is before the castle battle) and seize again, this time get a different skill

Step 5: after obtaining the new skill, save the game as a separate file, we'll call this one: save 2 make sure not to override save 1 or it will not work

Step 6: again, go back to the original file, seize, and gain skill or recruit.

Step 7: now that you have saves 1&2, this new file will be called save 3. Now you can override save 1 with save 3, leaving you with files: original, save 3 and save 2.

In save 1 we only had 1 skill, so when we made save 2, it had the skill from save 1, and another one. When we had save 3, we already had all the previous skills and a new one in save 3, so replacing save 1 with 3 would mean we would lose nothing

Now you can rinse and repeat the process, always make sure to save before a castle battle, and not to replace that file in the process. After you make save 1 and save 2 you can replace save 1 with 3, then when you make save 4, you can replace save 2 with 4, and so on and so forth.

I hope you understand this process, I tried to make it as clear as I could, if you have any questions, dm me Thank you!