Why such a large bleed? are you really expecting a 50mm misalignment in cutting?
I know, it is ridiculous. But it is the client request.
Thank you anyway.
I think you should talk to the client...
The only way around your problem that I can think of is to add a slug and put crops in the slug area manually, then include the slug in the export and don't make automatic marks, or change the page size so it includes most of the "bleed" area. 50 mm of bleed is absurd -- you either need a larger page because that bleed allowance is going to be used (for a casebound cover wrap perhaps, but that's still a lot), or somebody has miscommunicated a dimension someplace.