A good proposal.
While the SIS Spy is a good equivalent, it's not quite the same. I would suggest a republic aligned bounty hunter equivalent perhaps. Call it the enforcer or something.
Box of tricks tanking tree that resembles the BH, but uses more cryo rather than pyro. Make the medium armored version an out right spy design. All james bond gadgets and what not.
To lazy to copy/paste this into previous comment; your idea is VEEEERY good! For BH, most light-side choices involved putting a target on cryo, so this would be an easy fit. In addition, it can easily fill both the Medium Armor start, Medium Armor Tech Power Caster and Heavy Armor Tank. When I get some free time, I'll do a write up similar to the one I did for the Trooper above.