Right now, I am having trouble fiddling around with a Bounty Hunter-Hired Gun. Is this a possibility? I noticed in one or two episodes of Star Wars the Clone Wars which featured bounty hunters as central characters, one group acted as a bodyguard for a mysterious box. It is one that featured Asaji Ventress becoming a bounty hunter, I think. And since Hired Guns have Bodyguards as a career, I thought about merging the specialties together.

Is it possible?

You pick a career, but are allowed to buy whatever specs from any career you wish with the requisite xp expenditure.

In the full game, Hired Gun and Bounty Hunter are separate Careers. At that level, they can't be mixed. But each Career has six Specializations under it (where the real character distinctions come into play). You can certainly buy a Specialization from a different Career, provided you have one from your home Career already. (I.e., it would be a second or third specialization.)

So, if you wanted to make a character who is good at shooting big weapons and guarding clients, you might go Hired Gun: Heavy to start, and then buy a secondary specialization, the Bodyguard, which is in the Bounty Hunter Career. Your home Career would be Hired Gun, but you would have one Specialization from Hired Gun and a second one from Bounty Hunter. You could just as easily take a second Specialization from the Colonist Career, the Smuggler Career, etc.