[Fatt_Shade]

For skills to have 4/5th lvl`s you need to change also eng_skills.lng in loc_ses.kfs archive. because there is part of skills that are displayed in hero screen, and your 4/5lvl`s wont be available with just skills.txt changes.
Implement changes in your eng_skills_ext.lng into that file maybe game will accept them after that.

And couple Q :
1) Skills :
- endurance 4/5th lvl dont give any bonuses
- rage ready you make random orc unit lvl 1-6 get bonus adrenalin at start of battle (there ARE no 6lvl units)
- icy rage you have 1255 chance for your units to freeze enemy on hit . . . how do you even get something above 100%
- blood lust 85% permanent rage pool ?
- 35% for ally units to get 100% bonus attack, for 2 rounds , 100% crit with 100% more dmg from crit hit ... seems a bit overpowered
- runic power 100% bonus dmg from rage skills, with 100% chance to use it 2 times per turn

- weakness lore you give wrong bonus for ally crit% , pars=9%,9% and then in filter you give 7% crit bonus ?
- inspiration again same as weakness lore, bonus in pars and filter part arent same for 3/4/5 lvl`s
- tactics only skill i like change, -initiative to enemy but -2 for whole battle is to much, better make it just for first 2 turn on 5th lvl.

- linguistic +15 intellect, a bit much ?
- alchemist -90% crystal cost for upgrading spells ?
- accuracy you make skill that allows player to destroy items up to 7th lvl (param1) ,and create items up to 6th lvl (param2) with recipes.
- creator spells last +5 turns (param2) (blind,fear,slow ... ?)
- destroyer 90% dmg bonus AND 15% crit for spells.

2) medals :
- headhunter 5th lvl need 90 heroes killed. there are NO 90 enemy heroes in game
- dragon slayer 400 killed for 5th lvl ? is there so much dragons in game to kill ?
- mental executor/talented warrior need 500 enemy stacks killed with spells/rage skills !?
- fire_mage 5th lvl bonus is 65% in medals.txt , but in eng_rewards_ext.lng it says 60
- trapper max lvl give 5 traps, with +400% dmg
- vampire slayer need 13000 killed vampires ???
- holy knight 900 spells to get +5 attack/defense/initiative to 3 units (who would waste time on that)
- stupid/undead slayer 450 stacks killed for undead no prob they are all over this game, but 25 orc i`m not so sure
- blind rage 49000 rage used for 5th lvl, you`re kidding right ?
- strategist 5th lvl +4000 lds is a bit much, and 400 battles won with no losses, i`m not sure if there is that much battles in whole game (theLegend was around 330 , AP/CW 350 max)

I said this before to your mod for AP 5th lvl skills medal is interesting, but check what are you giving as params or rewards in medals before just simply slapping numbers in txt files (like 125% chance to freeze in icy rage skill, why would you need more then 100% for it?).