How do I do it? Is there any reason I shouldn\'t?
I have a winform ClickOnce App that has about 13mbs in DLLs that are not mine so I would have no need/ability to u
Although the other answers are correct, in that ClickOnce will only download DLLs once (if they have not changed) to address your direct question, if you will be installing dlls into the GAC outside of the ClickOnce process and don't want to download these DLLs via ClickOnce at all you can do the following.
Exclude those DLLs from the ClickOnce download by setting them to prequisite within the ClickOnce->Application Files settings.
When you do this, the ClickOnce runtime will check the GAC before download and make sure those DLLs exist.