If they regularly want to change between two or three known threshold values, they could make multiple copies of the alert and activate/deactivate the alerts as required.
But, if the alert is used in a dashboard as well, there is only really a one-to-one relationship there.
So either there needs to be a whole copy of the management module.
Or it could theoretically be created as a summary alert so that the alert status should only report the value of the active alert.
But there have been issues in summary alerts in 10.7 where one or more of the included alerts are inactive, the alert status does not work, this was fixed in SP1.