People where not able to answer me clearly yet, maybe my question was really not clear.
I will try to be more specific now:
I have a european 3DS working on 9.2, and a fully working emunand on 4.5 (I downgraded my sysnand, formated the emunand then got back to 9.2 with my sysnand backup).
I can boot the 4.5 emunand quite easily with the gateway exploit in classic mode (by pushing X button when asked).
Then I am wondering if there is any way to inject the 4.5 CFW with the devmenu inside the emunand, without having to mess up with my 9.2 sysnand. (maybe I am saying an incredibly stupid thing, please don't hit me

)