Using the info line
You can use the info line to change the pitches (and other properties) of one or several notes numerically.
If you have several notes selected and change the pitch on the info line, the changes are relative.
That is, all selected notes are transposed by an equal amount.
If you have several notes selected, hold down Ctrl/Cmd and change the pitch on the info line, the changes are absolute.
That is, all selected notes are set to the same pitch.