In Byos, under the Byonic node, and in stand alone Byonic, you can adjust the protease specificity to accommodate unknown cleavage sites and/or non-specific enzymes.
For a truly unspecified, non-specific search, leave the cleavage site box empty, set the specificity to "non-specific", and the missed cleavages to -1:
For a search with unlimited missed cleavages but a known protease, you may place a -1: