First of all, where is the CUT tool?! It's been replaced by the copy tool. You can now use that to copy between schematics.
- Open one instance of Eagle CAD with your target schematic (TARGET)
- Open another instance of Eagle CAD with the source schematic you're copying from (SOURCE)
- SOURCE: In the source instance, use the Group tool to select what you want to copy
- SOURCE: Click the copy tool
- SOURCE: Right-click on one of the parts and select Copy: Group from the contextual menu
- TARGET: click the Paste tool and paste your group wherever you want.