Older versions of packages for some routers


how to define in the feed, that only old version of package compiles for specific router ?

for example, ffmpeg 3.2 do not compile for router sagem2704v2,
but ffmpeg2.8 compiles.

In your own build environment, you can edit the package Makefiles and patches to compile older version for you, but there is no practical way to do that in the global repo.