I would make them keep their posts, unless ordered otherwise. That is, the only difference with present gameplay would be that they could go from a section to another of the wall (or wall tower) by walking on top of it. Maybe that could be the default path (while unposting them first would make them take the shortest path through the ground, which might be not shortest in time if one adds a time to go up or down).

Indeed one has to be careful with mainly two things: micro and snowballing. To avoid the first, one should get slaves through capture, trade, or bondage as automatically as possible. To avoid the second, besides the problems mentioned (limited amount/lifespan), risk of fleeing/rebellion should be up there. Issues like phenotypes or "immediate" conversion have to guide the actual mechanism for things not to be weird. There are basically two ways to introduce slavery: with just a number, or units. A number could be another icon besides population showing slave population, that could be increased by fighting (like Loot), either with a "slavemaster" present or not (that could be an andrapodistēs for the Greek factions, although I have to check if there's something more "legal"), by buying at the market, or by "converting" own workers into slaves (it should be better than just deleting what one doesn't need anymore). The number of slaves (which would also slowly decrease because of runaway slaves) would provide some economic bonus, but if it goes too high there's risk of rebellion (Gaia units could spawn somewhere in the territory, decreasing the number of slaves). This could happen if an army is obliterated and the free/slave ratio suddenly decreases too much (how this ratio should exactly relate to rebellions is up for discussion). Maybe they could be set free and transformed into workers to deal with that ratio (but at a food price, and maybe an "adaptation" cooldown or a count on how many are freeable at a given time). With units, everything would work quite similarly, just that instead of a bonus, one would use them for any task wanted (I'd keep using a different population icon for them). I guess what would need more explanation in this case is the capture mechanism, but this also depends if there will be a morale/loyalty system.

I think the repository you asked for is the .zip file posted by @Freagarach in the following thread: Just extract the container and you see the modded files on your drive. By changing those, zipping and uploading you're 'pushing'.

Actually a slavery system could make more expensive units useful again in a non-violence !   I’m specifically interested in the nonviolence mod !

I just saw your similar post... ... and got reminded on this topic: My problem with your proposal is that it shouts 'I minimize micro-management!' but in my game style it would lead to more micro-management bc units would not more be where I garrisoned them and sometimes I need all those 5 units at one place and then I have a problem.