readonly tablespaces - is update possible?

Hi Gurus,

If I put a tablespace in readonly mode, then I issue a select statement on a table from that tablespace, and then I issue an update statement on that table, will it be allowed? I have a big enough database buffer, say, and I do quite a few operations on that table and then once I put the tablespace back in read-write mode after say 4-5 mins, will all the transactions be moved to my datafiles that belong to that tablespace? Sorry, I have not tested this yet. Wanted your thoughts first.

Thanks

Samrat