If I understand you correctly, you are talking about changing every note value to the half of its original value - right?

Yes, there is a way.

1) In all empty measures, change the default whole rest to a real whole rest:

Selection Tool.

Select All. (all measures selected, in the entire piece)

Plug-ins menu > Note, Beam, and Rest Editing > Change to Real Whole Rests

2) Change all note durations to 50 % of original duration:

(Selection Tool, Select All)

Utilities menu > Change > Note Durations…

De-select {Rebar music} if it is selected.

3) Time Signature Tool. (Select All)

Double-click the selected, and change the time signature to 2/4.

De-select {Rebar Music} if it is selected.

4) When you are done, you can change all rest measures to default whole rests.

Plug-ins menu > Note, Beam, and Rest Editing > Change to Default Whole Rests

Perfect!  Thank you!