Tibetan alphabet is an abugida divided by groups of four syllables in tonally descending order.
The syllables can combine into ligatures with other syllables by either writing a (part of a) syllable sign above or below each other, making altogether about 15,000 possible combinations. Tibetan has ancient written tradition and an abugida ligature written as e.g. 'rgyud' may be roughly read as 'juhd', a syllable ligature of 'bzhi' as 'jih', etc.
Since Tibetan spoken in my environment differs greatly from its dialects spoken by native Tibetans elsewhere, I would very appreciate any answer(s) to the following question(s):
Do syllables retain their tonality in abugida when said in colloquial Tibetan speech? I know that the difference is not quite important for Amdo dialect of Tibetan, but what about other varieties of native Tibetan speech?
Is there any tone sandhi in Tibetan similar to that existing in Chinese?
Do combined syllables change their tonal quality when (a part of) an extra sign is written above or below a main sign?