This assumes that one is using the archetype char-gen method. I started off by giving each PC one bonus specialty (for a total of two per PC), as a house-rule.
I tracked earned XP during the campaign. The base rules have mechanics for improving skill level and/or acquiring new specialties, so my PCs were able to "level up", as it were, after a few sessions.
Someone suggested the house-rule of adding a specialty each time a skill reached C level. I began my campaign using this house-rule, but discovered as soon as PCs had earned enough XP to start increasing skill levels that it produced OP characters. It created a "reverse-double whammy" situation, where the PC was rewarded
twice every time a skill level was raised to C (once, with the higher skill level, and again with the added specialty). I didn't like how quickly my PCs were becoming super soldiers, so I abandoned that house-rule several sessions in. I even went back and removed any specialties gained through routine skill advancement.
IMHO, artificially adding more specialties to a starting archetype will result in OP PCs. I'm not a fan of that approach, but it may suit others' tastes better than the base rules.
TLDR Version:
- +1 bonus specialty at char-gen
- From then on out, base rules for earning XP and spending it on skill level increase OR adding a specialty
- Adding more specialties on top of the above creates OP PCs
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