This is something that occurred to me too.  I just finished the novel for the first time.

Remember
that Blatty intentionally alerts us to anagrams in the novel.  I think
there are a few at work regarding people's names.

Regan:
it's an exact anagram of 'anger'.  It also contains "rage," and that's a
word that Blatty uses often in conjunction with the demon.

Lankester—
a caster-out of devils.  Also, the first syllables of Lankester Merran
form "La Mer," French for "the sea."  Also a famous piece of classical
music by Debussy.  I have no idea if that's relevant.

Karras— a phonetic anagram of sacre, the French word for rite or ritual.  D. Karras, a phonetic anagram of "sacred."

Chris MacNeil— kneel (before) Christ.

Blatty also likes to play games with words I noticed, which is a delight. For instance, when Father Merrin first arrives at the house:

"As she turned around to face him, she saw him standing with his head angled sideways, glancing upward, as if he were listening— no, more like feeling; she thought— for some presence out of sight… some distant vibration that was known and familiar.  Puzzled, she watched him."

The first time I read this, the word "Puzzled" just leapt out at me because it's not what I thought it said at first.  With the capital "P," a "u" and two "z"s, I thought it said something else entirely.  Now that is a master stroke of subtlety.  I notice that he employs this technique quite a lot— substituting a more ordinary word for a contextually loaded word.  I can't think of other examples off the top of my head but I noticed it a lot as I was reading it.