The phrase "a regular substitute" is correct and usable in written English.
It can be used to refer to someone or something that frequently takes the place of another, often in a consistent or routine manner.
Example: "During the teacher's absence, Sarah was appointed as a regular substitute to ensure the class continued smoothly."
Alternatives: "a consistent replacement" or "a frequent stand-in".
I was told I would be treated like a regular substitute.
Mr. Correnti began working at the High School of Environmental Studies as a regular substitute teacher in September 1997.
Having been a regular substitute for Adrian Chiles on The One Show, the surprise is that the BBC isn't getting more from him.
Now Ms. Stettler's cello teacher is William Rounds, a member of the Boston Pops and a regular substitute with the Boston Symphony who also now teaches Ms. Gordon.
He was a regular substitute over the second half of last season, coming off the bench to score a stunning first goal for the club against Colchester, before being allowed by Pressley to start three of the Sky Blues' final four games.
Fresh out of college, I had joined CBS News two years earlier as a desk assistant and had become a regular substitute for Jim McGlinchy, Cronkite's clerk on the CBS Evening News.
The manager of Jay Leno, who himself was Mr. Carson's regular substitute host, planted a story on the front page of The New York Post in February 1991, citing the fears of unnamed NBC executives that Mr. Carson was getting too old and was in danger of being supplanted by Mr. Hall.
Under his new contract, he will continue to have a presence on "Today," serving as the regular substitute host for Matt Lauer.
Shandling had been the regular substitute for Johnny Carson on the Tonight Show, so he knew whereof he spoke.
The job, of course, went to the more mainstream Jay Leno, who had been Carson's regular substitute.
He is weekend anchor for broadcast and has been the regular substitute for Williams in recent years.
