How to make blocks of a specific type in a radius be replaced by another block?

Use the 'Search for block in 6*6 box' procedure preset. It uses three variables, (sx, sz, and sy), to determine the positions of blocks in relation to the source location, and then sets a 'found' variable to true if a block at the offset matches a desired block. Instead of using it to search for a block, you can replace the central part of the procedure so that it replaces the block at sx sy sz, if it matches a desired block. You can also configure the size of the box, or add a randomization aspect to it so it doesn't replace all of them.