Temporarily disable all table indices

Hello.

I need to perform a mass operation (UPDATE) on each table row. E.g. - modify
one table column:

UPDATE tbl SET tbl_text = MD5(tbl_id);

The problem is that if this table contains a number of indices, such UPDATE
is very very slow on large table.

I have to drop all indices on the table, then run the update (very quick)
and after that - re-create all indices back. It is much more speedy.
Unfortunately the table structure may change in the future (e.g. - new
indices are added), so I don't know exactly in this abstraction layer, what
indices to drop and what - to re-create.

Is any way (or ready piece of code) to save all existed indices, drop them
all and then - re-create after a mass UPDATE?