I just converted a mod (Race Balancing Project) from ESP to ESM so I can easily use its races with other mods.

Is there anything I should be concerned about ESM files?

Why did you do that? You could just esmify it and let other mods depend on it. Literally making it an ESM forces it to be loaded early in the load order, and as it is not only cosmetic mod but also a race rebalancing mod, that is ot good. There are other compilations available that contain all or most of RBP's races that do not overhaul the races.

what do you mean by "esmify it"?

if it stays as esp, when I modify other mods to use its races - when I re-open the mod in CS, they don't load the stuff from the esp.
seems like the only way to use RBP's stuff in other mods is to turn it into a esm.

Use ESP(s) as resources for another ESP (by temporarily making it a master file)

1. Launch Wrye Bash

2. Right-click on the source plugin and choose "esmify"

3. Launch TESCS, preferably with OBSE (default with Wrye Bash shortcut)

4. Choose the esmified source plugin and the plugin to become dependent on it (unless you are making a new plugin)

5. Make changes, save and exit.

6. Right-click on the modified (or new) plugin and choose "espify masters" (convenient in the case that multiple ESPs were esmified)
>> notes: 1) always make sure to espify esmified plugins after finishing with them 2) esmified plugins are distinguished with blue text


Edit: TES4Edit supports ESP mastery, so you can make changes in it without going through all of this esmifying business.

ohh .. sweet. didn't know about this function. thanks =)

Using Wrye Bash to "esmify" an ESP is no different than using Gecko to "convert to ESM". Gecko renames the file when you do, but that's not at all necessary and the CS/Game will treat an ESP flagged this way as a master and load it early regardless.

Provided RBP isn't making any changed to cells or worldspaces, you should be alright to leave it this way while working on your addition to it and for short tests in the game to make sure stuff works, but don't leave it that way to play for real.