Hi @Claudio, welcome to the forums!
To you question, there’s nothing preventing this from happening within the API. There are “guidelines” for how to use it - i.e. CVEI see here and here - one of which being that Validation is a read-only operation, in which case this might be considered “against the grain”.
But even “Validation” is a guideline and nothing you need to explicitly follow. Each stage is a number indicating the order in which to run your plug-ins, and you could add your own “Pre-validation” stage which involved scene mutations.
order = api.ValidatorOrder - 0.1
If you’re asking for opinion, then I believe you’ll quickly discover why you’d want to keep validation immutable and that your artists trust in the tool might waver if it’s making automatic and invisible changes to their work. Pyblish as a whole is generally read-only, with the one exception being Actions, primarily to keep its use trustworthy and failsafe.