Yes, folks have cleaned their filters - please ignore all the hyperbole here, but the instructions may be helpful:
For pre-filters, they seem to constantly come and go on Amazon so most of the links folks have posted lead to 404 errors - but in general the most basic pre-filter would be a piece of quilt batting cut to size, but you can get fancy and get one designed for an air purifier - just make sure the measurements match 
For your future info - the specs on the filter are in the manual, and here: