Level 5 is compulsory so the only value restriction that applies is you must do what's stated in the compulsory text. I checked the text and it specifically says "legs outside of arms in a straddle" while giving no option for legs inside. I think the value/general difficulty of an inside stalder certainly is the reason the committee decided not to write it into the text. Inside requires a pretty refined drop technique, whereas a straddle leaves more leeway. Also, an inside stalder could be dangerous if the athlete cannot control it from their shoulders and ends up doing a forceful skin the cat. This is all not in line with the goals of the compulsory program which is introductory gymnastics technique.
I would not even expect 90% of level 10s to use this technique...there is little reason to really, and even an early developmental tracked kid would be working on refining clear, toe on, straddle stalder and beginning many other skills before going to an inside stalder. That's kind of like going down a rabbit hole.
And I'm sure everyone is gonna say their level 3s already do this, or something. And maybe they do. But again be careful the kid isn't doing a clear seat circle and then sliding her legs out to kip because that doesn't count and is more likely what an athlete of this level is doing.