Hello brunoc68!
I haven’t ever tried to implement either of these kinds of restrictions. But since nobody else has chimed in, I’ll offer a couple thoughts:
The first challenge is akin to what we call field-value “validation” in database circles. For TiddlyWiki, I think you would need an “on-save” action: A Modular Action Mechanism For Tiddler Save Button
I think it may still be worth asking a bit about whether you’re committed to tags here, rather than to having a person field and a note-type field.
Tags are convenient, but when you have consistent field-like structure to your real-world task, separate fields are often the wiser choice. Having such dedicated “lanes” of information may really make things easier as your solution grows.
(For example, suppose you later decide that it should be possible for a tiddler/note to correspond to two people, or to two types, but only under certain conditions… Or you discover a good reason to add an additional tag to some tiddlers (“on hold” or “done” or “urgent”, whatever), but now your on-save validation process (making sure there are exactly two tags, one from each of two categories) would need to be reworked to allow this further kind of helpful tag. If your data is in dedicated fields, meanwhile, your solutions can be more precise and less fragile.)
The second idea is not as easy to address without more details.
Do you want tiddler edits in general to be impossible — like forever, and for everyone? So, if someone hits the check-mark in edit mode by accident, that tiddler is forever engraved in stone?
I’m guessing (hoping?) things are a bit more specific. How to achieve what you want depends on how “securely” (and for whom) you want to prevent revisions to (some category of) tiddlers (once they are generated and the first editing session is complete).
The easiest (but least secure) way is just to HIDE the edit button on tiddlers that meet a certain condition. This is an easy task with a custom stylesheet.
A smart person who understands tiddlywiki (including you ) can still find ways to modify the contents of tiddlers whose edit button is hidden. Is that a problem for your project?
Can you say more about why you want to prevent editing (for whom, when, and with what level of lockdown)?