I am new to this extension sort of thing, and when I tried to install either of them, I got a warning about compatibility issues.
If I ignore the warning, and attempt to install it anyway, and it does not work properly, would I be able to uninstall it, and resume using my version as it was before. Knowing SketchUp 17 is no longer supported, I would hate like the dickens to compromise my installation.
I took a quick look at those two extensions and I can see nothing in them that tests for SketchUp version, so I conclude this must be a warning from the Extension Manager that they are not marked as compatible with SketchUp 2017 in the EW database. The compatibility markings are set by the author of each extension, not by the EW itself or based on independent testing. Because the last code version of each of these is dated 2015, I suspect that the authors simply haven’t bothered to update their EW pages (no way to tell whether they have tested against newer versions of SU). I don’t have time to test them out myself, but I didn’t notice anything in my look at the code that made me think they won’t work in 2017.
To your main concern, though, installing an incompatible extension can’t permanently damage your installation of SketchUp. The extension may simply fail to load during startup (in which case you get a popup telling you so). It may load but fail to run correctly. In either case, as @Julian_Smith wrote, you can uninstall just the problem extension(s) to make SketchUp whole again.