Any changes to screen dimensions will apply to all applications running.

For that reason, plus the fact that the user may have a legitimate reason
for having chosen their specific resolution (think visually impaired users),
it's seldom (if ever) recommended that you change the resolution.

The usual approach is to resize the form to fit the user's resolution,
rather than vice versa. Check http://www.mvps.org/access/general/gen0002.htm 
at "The Access Web" for a couple of suggestions.

Normally you have two choices.  Design all forms so that they fit on the
lowest resolution user you expect to have or publish a minimum resolution
specification for your app so that those with lower resolutions at least
know that it is their setting causing the problem and not your application.

The resize code routines are another option, but they are better at making
forms larger on hi-res displays (totally unnecessary) and not nearly so good
at making forms smaller on lo-res displays (what you actually need).

The shortcomings at making forms smaller vary from form to form depending on
the kinds of objects you use (TabControls, SubForms, etc.), so you might
find that they do work satisfactorily in your particular case.  Don't expect
them to be a silver bullet solution though.