These cases you are asking about are all different, and I wish you had given the context. The thing is the combinations with "что" could be either adverbs, or conjunctions, or participles. I wish, though, you had provided some context, which could make the answer easier.
The participle "что" in the adverb variation "почти что" gives "почти" a colloquial style "shade". In this case, the word "только" can be used without participle "что".
"Пока что" - is a conjunction with the meaning of time: "at present time". It consists of two words and cannot be separated in this meaning. "Пока что с командировкой придётся подождать."
"Только что" is also an adverb, sometimes called "an adverbial composition": "Солнце только что село." "Он только что пришёл." (in the meaning "recently"). In this case, when it is an adverb, it is impossible to "disassemble" this adverb without loosing its meaning.
