How To Update 1000s Of Items In 50 Tables

Hi all,
I'm looking for a way to re-number inventory items. The items exist in 50+
tables, hundreds of fields and there are several thousand items. Maybe one
table could hold the list of old & new items, another table holds the list
of tables/fields to update? How can this be done without needing a million
individual update statements?

A brute force method may look like:
update table1 set field1 = newitem where field1 = olditem

update table1 set field2 = newitem where field2 = olditem

update table2 set field1 = newitem where field1 = olditem

Thanks for any input.