How to disable SSMS table designer timeout?
"...i'm changing a column in a 130 GB table from text to nvarchar(max)..."

Hi If you change a column and you expect that it can take considerable amount of time - I would recommend writing a Query.

Depending on you situation it could be as simple as "ALTER COLUMN" or as complex as "Creating temp table, coping all data, dropping table, creating table with new structure, copying data from temp table".

In any situation, having a script will allow you to run it without any timeout probably in you maintenance window (if you have one).

Regards,