As the title says. I get a lot of turrets, that due to a nearby ranked up turret, have lots of damage done but few kills, thus don't rank up. Would it be possible to put in an option to have turrets rank up via damage done rather than kills?

I've been goin over it. The problem is I don't track each turret in any list, I track kills which is in the entity data and or item with tags.
To record and track damage for each entity and then record that on items when picked up can explode inventory or I'll be having to tack entities and manage list and updated kills based on damage events and checking which entity damaged what so it can get a bit messy.
Unfortunately I am going to have to leave this out.

Reasonable. If I may make a stupid suggestion? So as they work now, you use tags based on kills or you round them to the kills for whatever rank it is. Could certain damage values make them rank up but track the ranks just as you do now with the kill counter? So if a turret gets say, 10,000 damage but doesn't have 50 kills it will upgrade to private and jump to 50 kills?

If exact setting is on then kills. Then when picked up it retained in the item and transfered back to entity but it can make the inventory blow out. If on fuzzy then just start from kills required to get that rank. No damage counter on entities and them there is problem of multiple biter types with different health. It may be a possibility to track damage later but its not going to be few lines of coding to fix and finishing off modmash splinter is taking priority.

Quite reasonable. I understand that programming this kinda stuff can be complex. I do love the mod and I can't wait to see what else you might do with it. Thank you for it and the others you are working on.

I have noted this request in the FAQ