Is there a way to limit which researches the enemies do?

Yes and no.

1. If you set the research rate to 1%, in practice, the enemy will not have a lot of techs.
2. If you are a modder and you want Castra to ignore certain techs or recipes, I have a flag for that, and I can add additional options like that.
3. Yes, it is possible for me as the modder to prevent certain enemy research; that's actually part of how the "disable enemy artillery" works; it should be disabling them both at the research and placement level.

So, the problem becomes, what kinds of limits? Everyone has a different view. I am open to feedback; if there are a solid number of users saying "technologies X, Y and Z are unfun, please add an option to disable them" - I am open to discuss it.

A big part of what's "limiting" is that I want this fork to preserve the difficulty of the original mod for those who want that while still offering bug fixes and general ease of use improvements.

What research or how do you think research should be limited?

Was thinking of providing a string setting, mostly for older mods that arent as often updated, since as far as I can see there is some possibility of certain mods forcing errors/performance issues if they are 'used' by Castra enemies

To clarify, you are looking for a way for players - not modders - to directly disable certain techs? There are a couple ways this could be done, all with drawbacks.

1. In-game settings text box - I could create a setting in-game that allows you to type in tech names. Problems: maybe typing a lot of potentially long tech names into a small box. Any tech that doesn't perfectly match the in-game string will not be disabled.

2. Create a companion "disabler" mod that would allow you to type in tech names to a text file; this fixes the "small text box" problem but requires you to download and install another mod. The "exact text match" problem remains.

Unfortunately some of this is just, this is Castra. The original mod author made the choices to do blanket tech copying, and that's a core part of the mod. I can work on mitigating that, but it's inherently an issue that I can't entirely fix without making massive changes, which I do not plan to do.