That would depend on if you screwed up the install. IE, if you wire it backwards and short something out, yeah, that wouldn't be warranty. Or if you fail to fuse it properly and that shorts something out, again, no warranty.
Basically the dealer has to show the modifications you made caused what ever failure they're trying to deny warranty work on. If you go in with a bad front wheel bearing the dealer has no chance to deny you over a DIY homelink. If you go in with a blown ECM and they see some half ass'd attempt to tap into a constant 12 volt power source that you butchered up a harness you might have some issues.
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