Thanks for your reply ProfOak !
Sorry, I wasn't accurate enough.
I know how to create slash-cmd in my addons but I would like to create a library of slash-cmd created and used in other addons (like /dcrshow for Decursive, /raresist for CTRA resist list, etc...).
This could be done in macros (by creating a macro and fill it with /raresist for example) but I already have tons of macro and I don't want to fill my screen with all of theses macros.).
Another solution could be to put the desired slash-cmd in the chat frame and then "apply/send/validate" the chat frame... but I don't know how to "apply" the chat frame