Use global variables across a vault

Things I have tried

Using dedicated note to hold YAML for each variable; using separate notes for separate variables.

What I’m trying to do

So, I need to have global variables in my vault agnostic to any plugin. For example, say I am watching a movie. I will create a page for that. I want to be prompted for a name (that is not the topic of this question), process it to a tag and then store both into some sort of global variables. Later, if I see a nice shot, I will take a screenshot and put it in another note that will have a template for this. Upon creation I want this shot-note to have a tag that is stored in a global variable (the tagged version of the movie’s title).

The idea is to specify the link to the tagged name once in a template so It is replaced with a correct tag even after.

In my solution I can’t find a way to reliable read these vars and, what’s more important, write new ones.