Saw a youtube vid where someone modified 7.62x54R from Berdan to boxer. Involved decapping, drilling a central flash hole, swaging copper tube into place to hold boxer, clean up burrs.
My concern would be a possible increase in pressure due to the extra flash hole.
I read something that suggested that a while back.
Regarding the rimfire reload kit, somebody needs to come up with a way to make .41 Swiss (10.4x38mm) rimfire cases.