Healing abilities vs. CR

If I wanted to change the healing abilities of celestials or the priests stat blocks in the new Monster Manual, how much is the challenge rating affected? For example if I want to increase the number of times the priest can use its divine aid bonus action would I then need to change the CR and/or HP? Is there a rule for this somewhere?

The guidance from the 2014 Dungeon Master's Guide for making monsters doesn't list anything for healing abilities, but does suggest for Regeneration-like abilities to "Increase the monsters effective hit points by 3 x the number of hit points the monster regenerates each round." Note that this isn't about increasing it's actual hit points, you just treat it as having a high hit point max for determining CR.

For example, if you have a monster with 100 hit points, but it can regenerate (or in this case heal) an average of 10 hit points per round, you treat it as having 130 hit points when determining CR.

How much this will change the monsters CR depends on a lot of factors, but in most cases it won't nudge the CR more than one place, if that, unless the healing is a huge amount. 

And if the healing is consistent too, like Regen.