What are believable sound changes?
Over time or in the face of external pressure (like contact with another language, for example), the sounds of a langugae can shift. Language-wide sound changes are not haphazard, but rather affect the language consistently. This isn’t to say that all instances of a phoneme must shift — but all instances of that phoneme in the same phonetic environment must change. This environment can be very specific: say, voiced plosives become voiceless when occurring between back vowels in word-final syllables. If you consider phonemes as sounds with a set of phonological features, then natlang-like sound changes occur when some of theme features are dropped or changed. Sounds usually do not randomly change all of their features (at once, any way). If you want a very radically different sound, then you may want to take your language through intermediate stages to get there in a believable fashion.
