No, you can't "lock" an RP.
What you can do:
Shut off auto restore point creation and make manual ones. To do that you have to disable the Task Schedular service.
This will increase the chances of an RP staying around for the maximum time which is 90 days before it cycles off.
An alternative to disabling the TS service is to lengthen the time between auto restore points.
SR settings and preferences are stored in the registry in the key HKLM\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\SystemRestore.
The intervals can be played with: To adjust the intervals, change the value of RPGlobalinterval from its default setting of 86,400 seconds (24 hours).
To cut this in half, to 43,200; to triple, to 259,200 - every 3 days.
As an FYI, any critical MS
update or software install thru MS
's installer wil create a restore point.
Regards - Charles