What happened to your 0A?
I haven't had any issues applying decals to any Yamato/Arcadia valks so far. I always use Mr Mark Setter when applying decals. I'm quite lazy and stingy with materials so I often take shortcuts. Like on the VF-1 I did all the panel lining, decaling, and weathering straight onto the bare plastic before applying any clear coating.
Doing the same with the 0S.
I'm curious about the size difference between the Hasegawa 0S decals and the Arcadia stickers. If there's only a small difference in size, I might pick up a few Hasegawa kits just to get the decals.