A little puzzled by your reference to buying 100 ISO negative film and processing at 200 as that is push processing which is a different thing altogether. If you are going to do cross processing then you will have to use a lab where you can talk to somebody to explain what you want or your film will be rejected or processed in the 'correct' chemicals and you will just get normal results. Small local (pro?) lab if such things still exist.
PS My brain cells should be grey (apart from the white matter), I just note you do not query the 'old' bit!
