In Pathfinder 2e, are ability modifier benefits to things like HP and trained skills retroactive?

In Pathfinder 2e, a character’s Constitution bonus affects HP total. A character’s Intelligence bonus grants training in additional skills and languages.

Are these benefits retroactive?

Examples:

  • If a character’s Constitution modifier increases from +2 to +3 as the result of an ability boost, does HP increase by 1 per character level? So a level 5 character going from +2 to +3 Con mod would gain 5 hit points for the ability score increase?
  • If a character’s Intelligence modifier increases from +1 to +2 as the result of an ability boost, does that character gain another trained skill and learned language?

Retroactive DM Edits

This question came out of another post on here of mine, so there may be some similarities. An answerer/commenter on that question suggested splitting it off, so here goes:

I’m a new DM, using Lost Mine of Phandelver to run a campaign. During the course of this adventure, I discovered what I deemed to be a plot hole, in that the path to Cragmaw Hideout (or Cavern, can’t remember right now) is portrayed somewhat as being unsuitable for the wagon, yet the wagon is needed to move loot. This isn’t the point, just background.

My solution was to say that “when you entered the clearing, you also saw another path which is wider and suitable for the wagon”. My question here then is whether retroactively adding a feature is an acceptable/appropriate DM action. I know the DM makes the world, and DM word is law (to a point). But realistically, should the DM ever do this, go back and “correct” something I. The past, or should they find another way to handle it?

My concern was that the PCs either wouldn’t or couldn’t find another solution, so I gave them an option. Is it okay to retcon like this?