What effect will reducing the size of a varchar column have on the database file?

We have a number of tables in our database that have VARCHAR(MAX) columns where a VARCHAR(500) (or something much smaller than max) will suffice. Naturally I want to clean these up, and get the sizes down to more reasonable levels. The 'how' to do this I understand: my question is what will altering these columns do to the pages and extants on disk? (There's lot of info out there about what happens when you grow a column, but having trouble finding info on what happens when you shrink one.)

Some of the tables have a very small row count, so I'm not worried about the cost of the change, but some are quite large, and I'm worried about them potentially being reorganized and causing a lot of blocking/downtime. In practical terms, I just want a way to estimate a maintenance window. In general, I'd like to understand better how the database engine behaves in this case.

Thanks in advance!