The OSP/CPMA mod allows for the replacing of one weapon / item with another. You can even remove all matching items from a map. There are plenty of other options available as well. Personally, I would start with OSP and see if that does what you want - www.orangesmo...org/download.html
NOTE: Changing the entities on a map without updating the BSP and AAS (bot file) may lead to strange bot behaviour.