Hello Rowan! You can use the following command line to install EndNote 21 without the EndNote Click browser plugin: msiexec /qn /i EN21Inst.msi USERNAME="<Your_Username>" PIDKEY="<Your_Product_Key>" ADDLOCAL=ALL REMOVE=EndNoteClick.
To uninstall EndNote 20, you can use the following command line: MsiExec.exe /X {86B3F2D6-AC2B-0020-8AE1-F2F77F781B0C} /qn ALLUSERS=1 REMOVE="ALL".
To uninstall EndNote 20, you can use the following command line: MsiExec.exe /X {86B3F2D6-AC2B-0020-8AE1-F2F77F781B0C} /qn ALLUSERS=1 REMOVE="ALL".