After many years modding the game for my own pleasure, I decided to share this mod on Nexus. It was created for several reasons: most undead creatures give mediocre rewards while they take way too long to kill. Several players also don't feel comfortable with the undead, so this mod replaces them with bandits. I avoided quest specific undead, but any quest that makes use of the levelled lists altered will have bandits instead of undead. Summoned creatures were not affected.

Note this means that even the generic undead used in some quests will be replaced by bandits, unless that quests uses unique NPCs. For example: many Aylead ruins will now have bandits inside walls; some Mages and Thieves Guild quests will also have bandits replace wraiths, zombies and skeletons inside dungeons. It won't affect quests at all, but it isn't at all lore-friendly, even if it does provide much enjoyment. Also note that necromancer dungeons will often feature bandits attacking necromancers due to them being from different factions... but anyone who has played Oblivion long enough will have seen stranger things happen...

The levelled creature lists modified can be check below:
LL1Undead100
LL1Undead25
LL1Undead50
LL1Undead75
LL1UndeadBones100
LL1UndeadBones25
LL1UndeadBones50
LL1UndeadBones75
LL1UndeadBonesBossLvl100
LL1UndeadBossLvl100
LL1UndeadEthereal100
LL1UndeadEthereal100Undercroft
LL1UndeadEthereal25
LL1UndeadEthereal50
LL1UndeadEthereal75
LL1UndeadEtherealLvl100
LL1UndeadEtherealLvl25
LL1UndeadEtherealLvl50
LL1UndeadLvl100
LL1UndeadLvl50
LL1UndeadZombie100
LL1UndeadZombie25
LL1UndeadZombie50
LL1UndeadZombie75
LL1UndeadZombieLvl100
LL1UndeadZombieLvl25
MG10UndeadBossLvl100
MG10UndeadEthereal100
MG10UndeadLvl100
MG14LeveledUndead
MS06UndeadEtheralCrewLeveled
MS27LL1Undead100
MS27LL1UndeadBones100
SELL2Undead100

Note: every list has "Calculate from all levels" and "Calculate for each item in count" options toggled.

Permissions:
You can use this mod to your hearts content. Just add a mention to the original mod if you will.

Compatibility:
Since only the aforementioned lists were edited, any mod that edits them will conflict with this one. The bandits and undead themselves were not edited, so any mod can still use the creatures, as long as they have their own undead creatures lists and don't use these ones. If they do, only bandits will spawn. The spawn points were not altered. I played this extensively for years and outside of a very few hilarious bandit spawns during quests, it won't affect anything at all.

Install:
Add the file to the data folder and activate it with the launcher or the mod manager. Doesn't require anything, doesn't have any dependency.

Uninstall:
Just remove the file and that's it. You don't need to start a new game for the game to revert back to the original lists. The next time creatures of these lists spawn they'll be the default ones from vanilla Oblivion (or any other mod you use) and not from this mod.