(What can I say? Storm-and-pollen weather makes me peevish.)
Today’s peeve is another entry in the Homonyms to Watch Out For competition: alter and altar. Not the same thing, folks. To start with, one of them’s a verb and the other’s a noun. Beyond that—
To alter something is to change it. The adherents of the Arachnophagic Heresy of the Cult of the Great Spider angered the orthodox Spiderians when they attempted to alter the liturgy.
An altar is a table or flat-topped block used as the focus for a religious ritual. The orthodox Spiderians disapproved of the Arachnophagists’ practice of setting up the main altar as a dinner table, with the centerpiece being a platter of deep-fried tarantulas.
It all ended badly, of course. The attempt to alter the Spiderian altar resulted in the terrible and bloody Spider Wars of the Fifth Age, at the end of which the Cult of the Great Spider was no more.
Dr. Doyle's Blog 
I haven’t encountered that mix-up, but the books I read that mention religion all have to do with actual practices, so the writers and editors of those works must be more aware of what appears on the page. I mention editors, because I recently read a short book that purported to have been professionally edited and published, but it was pitted with at least a dozen glaring spell-checker gaffes. An indie who publishes such highly defective work looks foolish, but a professional who does so is a fraud.
Bad stuff can happen sometimes . . . I’ve heard horror stories. Things like the uncorrected galley proofs (which haven’t been typeset in actual physical hot-lead galleys for decades now, but the terminology persists) getting sent to the printers instead of the corrected ones that the author sent back in, or copyedits from hell where the copyeditor “fixes” stuff that doesn’t need it and misses the stuff that does, and the author is so frantic with trying to un-fix all the fixes that the real, uncaught mistakes go unnoticed.
(Copyeditors are a noble and hardworking tribe, by and large, and a really good one is far above rubies . . . but it’s one of those jobs that the general public only notices when somebody screws up.)