I think I wasn't clear enough phrasing my question.
I'm aware of the script and I'm using it, but for the option [-AutoDelete <EFreeBackupRetention>], is it possible to use other values than:
Never
Tonight
TomorrowNight
In3days
In1Week
In2Weeks
In1Month
No, there are no other values that can be used except for those that you've mentioned. For custom retention settings you'll have to create your own script that applies the desired retention rule.