Reservation script in WFA commands can be treated as a way to simulate the effect of the particular command on the WFA cache. Since the commands effect can only be really seen after the next cache acquisition, reservation script is used till then. When the next cache acquisition occurs and the data is present in that(this validation is done using the Verification script), the reservation entry is removed. Yes, you are right, you can see reservations as a temporary update to cache until, cache acquisition occurs. You can use INSERT and UPDATE commands as necessary. For example, if you look at 'Create Volume' command's reservation script, you can see that there is an 'INSERT' statement to insert the entry into the 'volume' table. And an 'UPDATE' statement to update the 'used/available' space columns in 'aggregate' table.
