It is possible. I do not know how often and when VRS does it but the program do re-read the registry from time to time. I have frome time to time changed my schedules directly in the registry and VRS have picked up these changes without me having to restart the program.
In order to write a php script to generate a registry file you must only follow the "rules". Here's the recording schedule for one of my channels. It will give you a clue to how the scheduler entries is built up.
One thing to remember: If you reduce the number of scheduling entries you must also delete them from the registry, not only write a reg file with the new entries.
Example of registry:
[HKEY_LOCAL_MACHINE\SOFTWARE\NCH Swift Sound\VRS\datetime2]
"count"="4"
"commence0"="24/09/07-00:00:00"
"expire0"="24/09/20-00:00:00"
"todstart0"="07:00:00"
"todend0"="07:03:00"
"weekdays0"="62"
"commence1"="24/09/07-00:00:00"
"expire1"="24/09/20-00:00:00"
"todstart1"="10:00:00"
"todend1"="10:03:00"
"weekdays1"="62"
"commence2"="24/09/07-00:00:00"
"expire2"="24/09/20-00:00:00"
"todstart2"="13:00:00"
"todend2"="13:05:00"
"weekdays2"="62"
"commence3"="24/09/07-00:00:00"
"expire3"="24/09/20-00:00:00"
"todstart3"="17:00:00"
"todend3"="17:10:00"
"weekdays3"="62"