the first bit, i believe they would have to have a lot of money to bribe officials. cause technically the character would be a halfblood, but the child of muggleborn parents, and durmstrang is known to refuse muggleborns.
for the second question at least, we're not adding any more schools to MH at the mo', so a pretty low chance. there is possibly a chance for an alternate school available for reference, but it wont be playable.