I believe that existing rules imply the existence of consecrated ground not created by the hallow spell (see Are there published effects of Consecrated (not Hallowed) Ground?)
I am currently running Curse of Strahd, and would like to have some of the churches be merely consecrated ground, and others be hallowed (which would be a stronger effect).
Since there does not appear to be at present a rules description of the effects of consecrated (but not hallowed) ground, for the purposes of my game I would like to treat consecrated ground as
Undead standing on consecrated ground have disadvantage on all saving throws
(to mirror the effects of desecrated ground in the DMG) and
Undead standing on consecrated ground take d6 radiant damage at the start of their turn
(to mirror the DMG description of holy water purifying desecrated ground, to provide a cinematic effect of Strahd zombies bursting into flame as they attack a church, and to provide PC’s a safer zone where they may be attacked by vampires and vampire spawn but at least their foes can’t regenerate)
To balance this second effect I would add the following to the effects of desecrated ground as described in the DMG:
Celestials who use their Healing Touch while on desecrated ground have it count as two uses toward their daily limit.
Would providing these benefits to the consecrated ground at the various holy sites within Barovia disrupt any plot points or unbalance any encounters within Curse of Strahd?