Per page 93 of Edge of the Empire, a player can add specializations from any career using experience points earned in play.
Specializations within one's Career are cheaper to purchase with earned XP. Specializations from outside one's career come at a higher cost, but provide access to the Specialization's Talent Tree, as well as the small set of additional Career skills listed with it. Some specializations are listed as being "Universal" specializations which set their cost as being the same as those from within the character's career. The cost for purchasing a new specialization, either career, non-career, or universal increases with each addition. In Edge of the Empire, the universal specialization is Force Sensitive Exile, Force Sensitive Emergent, and Recruit appear in Age of Rebellion. Force & Destiny may add another.
Bounty Hunter (Career Skills: Athletics, Brawl, Perception, Piloting (Planetary & Space), Ranged Heavy, Streetwise, Vigilance
Gadgeteer (Career Skills: Brawl, Coercion, Mechanics, Ranged Light)
If the player sought to see the character develop in the Force after meeting and spending time discussing the universe with a strange old woman on an Outer Rim planet, they might choose to spend their earned XP on the Force Sensitive Exile career specialization. This works in the same way as adding any other specialization.
Doing so will provide them with access to working with the Force (Rating 1) as they did not previously have a Force Rating. They will also gain access to the Talent Tree for the Exile. The specialization has no Career Skills, but if it did, the character would have access to those as well. As a universal specialization, it costs the same as adding a Specialization from within the Bounty Hunter career.
Later, if the character was constantly working with Smugglers, they might pick up a Specialization from that Career, such as the Scoundrel, acquiring access to the career skills and Talents associated with it. This is an out-of-career specialization for the Bounty Hunter, and so will cost more.
As noted above, each additional Specialization added becomes more expensive in terms of XP cost, regardless of source.