For building an Operator as a tech-specialist? Well, demolitions specialist more like, but explosives fall under Tech-Use, soo...

Our entire squad are Guardsmen, no Specialists, so I decided to make an Operator who specializes in demolitions and minor repairs.

Seeing as my chance, on an unmodified test, to set up any explosives (Int 32, Tech-Use is Trained) without incident is 42%, and the chance of it going off in my hands is something like 28% (unless I'm flubbing the math?), I was looking to improve that. I feel it's slightly... ah, risky.

Are there any things that are good for that, besides just buying some Int increases and higher levels of Tech-Use?

Since Tech-Use uses Intelligence, Commerce and Logic would complement well, giving your squad some added help in Requisitions and gambling, respectively. Medicae is helpful if you don't already have a Medic, though it won't help too much if your patient is already in critical.

Don't overlook Common/Scholastic/Forbidden Lore skills either - they might need you to think creatively, but are used to get hints about your surroundings, enemies, or tactics from the GM.

Been playing an Operator myself. They are the god-tier support guardsman. Grab yourself a sniper rifle, some equipment to aid your work, and cybernetics to grab the Flesh Is Weak to improve your durability in the field. Commerce is obscenely useful - I was dual wielding plasma pistols in carapace armour, to give you an idea of how crazy a powerful intelligence based character with good Commerce can be.

Ultimately though, what you want is to keep out of the line of fire, keep some distance between yourself and the enemy, and crank your value to the squad as a support character to the maximum so that they go out of their way to defend you.

Modify Payload, Bombardier, Foresight - think about something for 10 minutes to gain +10 on next test, have your sergeant yell at you, to gain another +10, Battlefield Tech-Wright - no penalties for distraction, Mastery,

Buy tech-use up. Your % chances include a combi-tool, right? If they don't, don't forget that they have one of those. Also, you get an auspex as part of your gear, you should take the skills you need to use that as it's pretty neat.