Have you considered using a Staff style to transpose just that measure?

Not sure how I would do that. I don't see anything about transposition under Staff styles. 

FWIW, Depending on the age of the musicians, I might recommend keeping the transposition intact in their parts for all members of the band. It will be very confusing if they switch to concert pitch with younger players.

… Not sure how I would do that. I don't see anything about transposition under Staff styles …

Staff Tool.

Staff menu > Define Staff Styles…

Come to think about it:

Since each transposition would require a separate staff style, you can not use a single “Staff style to transpose just that measure” (quoting J Adrian Verkouteren).

Instead of using multiple transposing staff styles, consider using a single staff style that selects “Ignore key Signatures” (in the pane Behaviors, see my screen shot above).

This step will move the measure to the key of C major.

Copying music to and from the other measures will be a little tricky, since the music will be transposed during the copying.

You can use the utility to transpose the music (back) after the copying.

Peter is correct that one would have to set separate Staff Styles for each class of transpositions. (One style for major-second Bb instruments could be used on Trumpets, Clarinets, etc.)

Also realize that showing notes in concert pitch will not necessarily make them sound in concert pitch, so you may want to write those notes in a separate Layer that you keep muted in the Score Manager. (I habitually use Layer 4 for muted notes.)

Thank you very much for your helpful suggestions! I did manage to make it work!