Can I make entries using an assembly .dll to a config file named .exe.config which belongs to myservice.exe?

Can I make entries using an assembly .dll to a config file named
.exe.config which belongs to myservice.exe?

I Have an assembly for encryption of a user input written in c#.net.
During installation user password should be encrypted and written to
myservice.exe.config file which belongs to myservice.exe. I have
myassembly.dll, myservice.exe and myservice.exe.config in the same folder.
Will that be possible??? If so please guide me how to achieve that.