As far as I'm concerned, to go to V5.3, as according to the official P3d website, it says this.
https://www.prepar3d.com/news/announcements/2021/12/120925/
They are saying they recommend to fully uninstall previous version and reinstall to V5.3.
Nowhere it says you are also required to uninstall all the add-ons, which is what you said you didn't want to "lose".
I think LM suggests that method, but only to be sure users will update the Content and the Scenery as well, meaning using the Client only won't work. However, you can just install the Full installer over an existing installation, and it will usually work, a complete uninstall is rarely required.
But even in case you would need to Uninstall, I also replied with this case:
At least those that don't modify core files of the sim by overwriting them, which is a practice that is really useless (and whatever add-on still using it, exposed to public shame) in P3D, since with the add-on.xml method, any file can be overridden without having to change any file of the simulator.
Proper P3D add-ons that don't modify any files in the sim, are possible since the add-on.xml method has been introduced with P3D 3.4.
Those add-ons can survive even a FULL uninstall/reinstall of the simulator with no issues, because on the next restart, provided their add-on.xml is in the correct "auto-discovery" folder, which is the Documents\Prepar3d Addons folder, you'll be asked if you wanted to reactivate your add-ons.
GSX of course is fully compliant with this, and most of the more recent add-ons also are but, if you still have add-ons using legacy installation methods inherited from FSX, which places their files directly in the simulator own folder, you can use something the popular Lorby's Addon Organizer ( P4AO ), which can convert those add-ons to the add-on.xml method, which will make updating the simulator easier.