Don't blame me if I'm wrong
but if you can spoof to 5.5.0 to play games that have an update on disc, I don't see any reason at all why Loadiine would treat it any differently. If you want to wait for confirmation or otherwise from another member it wouldn't be unwise.
Spoofing is not revertible. Basically, the Wii U has a version.bin file that tells what version you're on. Spoofing overwrites that file to say "5.5.0" instead of "5.3.2" so that when a game with 5.4.0 or 5.5.0 asks your system what version you're on, it thinks it's 5.5.0 and will be happy and still launch without wanting you to install a system update. AFAIK, this version.bin file can only be incremented (I thought
@SonyUSA said there is a way to delete it and write a new one back to 5.3.2, but if something goes wrong you have a brick), so the only way to get back to a "normal" system is to do a full update (the rest of the system files) to 5.5.0 or whatever future FW comes out.