You will find plenty of folks here that'll tell you not to mess with the ROPS.
If you are in a real crisis on the issue, I would either see if there is a folding Kubota ROPS from another tractor, perhaps, that has a similar mounting scheme.
Or scrutinize a Kubota ROPS and have a modification done professionally by a local machine shop.
I only suggest this because this is a better alternative than having no ROPS at all, as it seems you have right now.