Insoles

Not without care. A safety boot is certified as a complete product, and on boots with a penetration resistant insert the insole is part of that certification. Replacing it with an aftermarket insole can invalidate the rating. Replace like for like, or use an insole the boot maker supplies for that boot.

It makes it more comfortable, not more protective. Once the toecap has taken a real impact or the tread has worn through, the boot is finished whatever you put inside it.