The phrase "alternative letters" is correct and usable in written English.
It can be used when referring to different letters that can be used in place of others, often in contexts like coding, linguistics, or creative writing.
Example: "In this puzzle, you can use alternative letters to decode the message."
Alternatives: "substitute letters" or "replacement letters".
Another approach to rate-enhancement is Dasher, which uses language models and arithmetic coding to present alternative letter targets on the screen with size relative to their likelihood given the history.
To that end, and in keeping with Rule #84, I have compiled an alternative letter of advice from Diane Ravitch to Lamar Alexander about NCLB -- the text of which is composed, word-for-word, from Diane Ravitch's writings about education over the last four decades.
For the second aim, we compared the influence of the original PHS invitation letter with the no-letter group, but we also developed an alternative letter.
Each exact match between an amino acid and the search pattern produces a score of 1, whereas a match to an alternative letter only scores 0.4.
In this alternative letter, the informational content was similar to the original PHS letter but the content was simplified and adapted to decrease possible negative associations and promote a more positive attitude towards chlamydia (see The invitation letters).
Over the decades, synthetic biologists trying to expand life's genetic alphabet have come up with a handful of alternative genetic letters.
As an alternative, cut letters out of construction paper and paste them to your sign.
But state regulations explicitly allow an alternative: a letter from the Social Security Administration confirming that the applicant is not eligible for a number.
The letter said the boycott was meant to show both of the groups' displeasure with the latest actions by PayPal and the F.B.I. "We encourage anyone using PayPal to immediately close their accounts and consider an alternative," the letter said, adding that PayPal's apparent willingness to work with the F.B.I. "should be proof enough that they don't deserve the customers they get".
More evidence is needed on whether screening behavior can be increased by the use of an alternative information letter adapted to the specific unconscious and conscious determinants revealed in this study, or that we need other, more interactive behavior change methods.
