Editing compiled assembly C # resource file

I have a resource file where I store a connection string, etc. for class library (I can not use App.config, do not ask why!?!). It was my assumption (maybe it's stupid) that I could change the .rex file of the file on the assembly at runtime to be able to change the connection string through the environment without recompiling the assembly every time, someone can check my assumption and, if maybe tell me how to do this?

Greetings