Some roles of Grace's family were recast for the reboot. Grace's sister Janet Adler was previously played by Geena Davis in The Accidental Tsuris (2004), she is now played by Mary McCormack. Grace's father Martin Adler was previously played by Alan Arkin in It's a Dad, Dad, Dad, Dad World (2005), the role now played by Robert Klein. The role of Joyce Adler (Sara Rue) was played by Rue for both the original run and reboot.
Grace and her sisters sing the song their mother (played by Debbie Reynolds) always sang to them on their birthdays. The song, "All I Do Is Dream Of You" was sung by Reynolds in Singin' in the Rain (1952) .
Robert Klein plays Debra Messing's (Grace's) father in the reboot, he also played her father in The Mysteries of Laura (2014).
Malcolm Widmark, played by Alec Baldwin, says he learned to match his pajamas to the drapes to blend in by "His Homey Comey." This is a reference to James Comey and his avoidance of Donald Trump prior to being fired as FBI Director. Baldwin famously portrayed Trump during his four year presidency term on Saturday Night Live (1975).
The reason for recasting Alan Arkin and Geena Davis is unknown; however, it is possible they had scheduling conflicts in The Kominsky Method (2018) and GLOW (2017) which prevented them from returning for occasional Will & Grace episodes in the revival run.