If Approver is a role that will be used for granting approval rights to a user, then executing the following

1. Edit futuretense_xcel.ini and set xcelerate.grant.approve=Approver
2. Restart the server for the change to take effect.
3. User1 is given Approver role and User2 is not given this role.

will allow User1 to approve an asset and deny User2 from approving an asset.

If Approver is a role that will allow approving and DnApprover is a role that will deny approving, then executing the following

1. Edit futuretense_xcel.ini and set xcelerate.grant.approve=Approver and xcelerate.deny.approve=DnApprover
2. Restart the server for the change to take effect.
3. User1 is given Approver role and User2 is given DnApprover.

will allow User1 to approve an asset and deny User2 from approving an asset.