In the Constrained Atoms panel, I can only modify the force constant and half-width for one atom at a time. How can I adjust the constraint parameters for multiple atoms?

The way to do this is to define the desired constraint parameters prior to selecting the atoms, using a Maestro command as follows:

1. Import your structure into Maestro.
2. Open the MacroModel panel for the desired calculation type.
3. In the Constraints folder, click Atoms.
4. In the Command Input Area of the main window, enter the following command:
   
   constrainedset constant=value width=width

Use the desired values for value and width. The usage for this command can be found in the Maestro Command Reference Manual. If the Command Input Area is not visible, you can display it from the Maestro menu.
5. In the Constrained Atoms panel, click Select to open the Atom Selection dialog box and choose the constrained atoms. When you click OK, the list is populated with the atoms that you selected, and by clicking on a row you can see that the constraints have the parameters you entered with the constrainedset command. Repeat steps 4 and 5 of this procedure for as many sets as you like.