Oh, I see what you mean! Thank you for clarifying.
And to get it out of the way, I’ll answer your second question first: When you use the Specialist 4th Level perk, you take a Class Tag as if you had the class, and you can upgrade it as you would any other tag. Easy peasy. Use it as if you had the associated Class Move, as well.
As for the Psionics question - this is where things get rather vague, and I fear I may give a bit of a cop-out answer. Simply put, I would leave that to be house-ruled at your table as you please.
But I want to be more helpful than that. So I’ll give a couple of examples of how I might resolve the rule at my table.
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Do as you say. When you activate Guile 2 via Psionics 3, you replace “Approach” from the Guile rules with “Effect.” Presumably, whichever effect you’re Casting Magic with at that moment.
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Treat the Guile activation as if you were Influencing Someone. So pick an Approach to use, and apply your Trick to that approach for the duration of your Cast Magic.
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Split your rolls. Make your Cast Magic roll to attempt to charm someone. On a success, then make an Influence Someone roll, with Guile 2 and the Approach tag of your choice; whether you use your social or mental stats for the latter roll would be another matter of table ruling.
Generally speaking, gaps in the design like this one are left there on purpose. It’s the kind of space I love to see as a player - it lets me use my imagination and shape the world of the game to my imagination. Rule things in ways that are fun for your table, and ignore anything that doesn’t speak to you.