I've looked at the cupstages file; spin recovery is only activated at "beginner" difficulty and opposite lock at "beginner" and "novice", which I never use.
I've tried your suggestion anyway, but as I expected it is not the remedy.
As I've mentioned, I only encounter this issue with the HQ Mod installed - with either the vanilla game or the standard 10th Anniversary Patch install it does not happen and if I uninstall the HQ Mod it stops happening as well.
As noted before, even simply starting and then immediately quitting GTL triggers the effect.
Setting the PLR file to "read only" is no solution, as the game removes that flag.
[EDIT]I think I've found out what the problem is; in the cupstages.cdb file in the HQ Mod several lines are missing under the "Assist" category in the various difficulties, namely "SteeringHelp", "ThrottleControl", "AntilockBrakes", "SpinRecovery" and "OppositeLock".
I've added these lines to all difficulty categories (copy/paste from the standard cupstages file in the 10th Anniversary Patch) and now the issue seems resolved - spin recovery and opposite lock stay at "0".
NB: these missing lines do exist under the "Digital Throttle Assist" and "Digital Steer Assist" categories, but I suspect those refer to keyboard inputs and apparently the entries need to be listed under "Assist" as well, otherwise the game will fall back to a vanilla state of "1" unless these functions are turned off in-game (and as far as I know there is no way to turn off opposite lock and spin recovery in-game).