My best guess is that GEN is for GENERIC (type of the aircraft) 
PS : It doesn’t reply exactly to your question, but at least if you want less obstrusive label : [UIMOD] I want to introduce my mods to you
My best guess is that GEN is for GENERIC (type of the aircraft)
PS : It doesn’t reply exactly to your question, but at least if you want less obstrusive label : [UIMOD] I want to introduce my mods to you