I'm thinking it should be possible to have a selection tool (similar to say an upgrade planner), that open the same dialog as when you install a blueprint. Letting you set blueprint variable later on.

The specific usecase im thinking, I have a blueprint for a semi automatic factory that handle producing 40 stacks of any item select. Each blueprint can produce up to 6 different items. Which i use blueprint variable 1-6 for.

Say i install the blueprint, select "fast transport belt" for variable1, and leave variable2-6 unchanged.

Currently if i then want to add "fast underground belt" to it, i have to manually edit each variable2, or destroy the whole thing and replace the blueprint to then select the fastbelt on 1, and the underground on 2.

Id like to just grab the blueprint variable selection tool, select my factory, and then change variable2 to underground belt. leaving 3-6 as is, until later on id change 3 to a new item etc.

To be clear tho, im not talking about being able to change the same variable over and over, that would imply tracking which one was what before the change. All i suggest, is the option to change previously untouched variable.

i ended up doing a quick and dirty version as proof of concept. Good enough for me, im too lazy to go setup a github account just for it so here
https://file.io/pfCDjQPpnAUj

feel free to do what you wish with it, it add a shortcut (blue background yellow star), that when you use it, you can select over existing stuff and replace blueprint variable the same way you would on a fresh blueprint.

Edit: theres a few dirty skip / hack / crash in this version, its really just a proof of concept to explain what im suggesting. I do not recommend anyone try using it unless they are ready to spend time fixing it for whatever crash theyll personally experience. It is working for my specific use case, but im confident it will crash for anyone trying to use it regularily heh.