Special Modifications (Pg 94) adds rules for a workshop. Not only does this count as always having the right tools for the job (for a single skill), but advanced benefits can downgrade the difficulty of the check once and grant boosts on future checks in the right circumstances.

Stay on Target (Pg 45) has a Custom Tool Kit, which adds a boost die to repair or maintain a specific item/vehicle. Your GM could allow that to apply to modding a specific weapon's attachments.

Keeping the Peace (pg 53) adds the Jedi-Multitool, which adds an automatic advantage to checks to mod or repair lightsabers.

Special Modifications (Pg 52) and Fully Operational (Pg 48) both add the Intelligent Toolbox, which reduces the time for crafting and other mechanic related checks by 50%

Savage Spirits (Pg 49) adds the weapon maintenance kit, which adds 2 boost dice to checks to repair or modify a specific weapon type (slugthrower, blaster, etc)

Using a droid or NPC with higher ranks in Mechanics, or higher Intellect than you for a skilled assist check, augmenting your Int and Mechanics with whichever is higher of theirs.

The crafting-focused specializations also have a variety of talents that can improve your odds of succeeding on crafting/modifying.