[yocto] How to set SRC_URI in local.conf / how to set any variable of a specific recipe in local.conf

[Jakob Hasse]

Hello,

how can I set a another branch, i.e., the SRC_URI variable for a 
specific recipe in conf/local.conf? Or more general: how can I change 
the variable of any recipe in local.conf temporarily? I tried something 
like this already:
SRC_<recipe-name> = "..."
SRC-<recipe-name> = "..."
SRC_pn-<recipe-name> = "..."

I would like to switch a recipe to a testing branch temporarily via 
local.conf without playing around in the actual recipes.

Thanks and all the Best,
Jakob