As you indicated, this is the likely result. I'd like to see the video but looks like it's not available anymore.You will need to eliminate the "screw-on" engine retainer. If you don't, it will be impossible to insert the Stage Coupler for the Booster.
You will need to use or make an Engine Hook to retain the motor at Ejection.
You will also need to trim the rear part of each fin tab ( about 1.5" ) to allow the rear Centering Ring to be moved forward. This allows the Stage Coupler on the Booster to slide into the Airframe.
Here is a STAR ORBITER build thread. It may be helpful in planning your modifications.
https://www.rocketryforum.com/threads/estes-star-orbiter-9716.134806
A two-stage build thread . . .
https://www.rocketryforum.com/threads/star-orbiter-should-i-or-shouldnt-i.141542
STAR ORBITER instructions :
https://estesrockets.com/wp-content/uploads/Instructions/009716_STAR_ORBITER.pdf
ADVICE : "Measure TWICE, cut ONCE" !
Dave F.
https://www.rocketryforum.com/threads/star-orbiter-should-i-or-shouldnt-i.141542/post-1715472