Multiple original cast members were unable to return due to a number of circumstances that have occurred since the end of Mighty Morphin' Power Rangers:
- Thuy Trang who portrayed Trini Kwan, had passed away in September 2001. As such, this special is specifically dedicated in her honor with the story revolving around Trini's daughter, Minh Kwan.
- Austin St. John, who portrays Jason Scott, had been arrested for legal issues in May 2022 and put on probation, which prohibits him from traveling other than for convention appearances.
- Jason David Frank, who portrayed Tommy Oliver, declined to return for the special as he was dealing with a series of personal issues at the time. The actor sadly had passed away in November 2022. Furthermore, Frank had previously expressed his intent to distance himself from Power Rangers to focus on his lead film Legend of the White Dragon, which was posthumously released on what would have been his 50th birthday. Like with Trang, Once & Always is also dedicated to Frank as well.
- Amy Jo Johnson, who portrays Kimberly Ann Hart, was asked to return and reprise her role in the special, but she ultimately declined due to unspecified reasons. Despite so, Johnson did however announce her collaboration with Boom! Studios to write an original comic series for the franchise's anniversary.
The title of this series is derived from the phrase "Once a Ranger, always a Ranger."
Alpha activates the "Bandora Protocol," which is named after Witch Bandora, Rita Repulsa's counterpart from Dinosaur Squadron Zyuranger (1992). Furthermore in said scene, the computer screen shows several place names in the Power Rangers universe, namely: Coral Harbor from Power Rangers Beast Morphers (2019) Reefside from Power Rangers DinoThunder (2004) Astro Megaship from Power Rangers in Space (1998) Terra Venture from Power Rangers Lost Galaxy (1999) Turtle Cove from Power Rangers Wild Force (2002)
When accepting the proxy power coin, Kat says that she doesn't care if "too much pink energy is dangerous." This echoes a line spoken by Zordon in the original series in Wild West Rangers: Part II (1995), when Kimberly has traveled back in time and takes the original Power Coins of that time period to give to ancestors of the Rangers to defeat monsters attacking their old west town. Zordon warns against using the duplicate Pterodactyl coin, stating that "too much pink energy is dangerous." The line has become a popular joke among the online fan community.
Before the end credits, a musical tribute to the original Rangers is seen. The footage is taken from The Song of Guitardo (1994), one of the final episode to feature Tommy as the Green Ranger. The song is called "Down the Road" and is an original composition by Amy Jo Johnson. It was originally meant as a tribute to Tommy's time as a Ranger, which at that point seemed to be drawing to an end.