I tried to create a draft for new definition of {ze'ei} of MAI.
Definition:
Change the meaning of the first word within the semantic span of ze'ei-cluster, without changing syntactic role of the word. The new meaning of the word is the same as the word followed by {bu} forming the ze'ei-cluster.
Notes:
Usually, ze'ei-cluster has a form "X bu ze'ei", where X is any lojban word other than the words of selma'o ZO or FAhO. A ze'ei-cluster is usually put at the beginning of the definition of a word, and the semantic span is the whole line of the definition. Just like definitions of most cmavo, the definitions by ze'ei are not to be used to expand the defined word appearing in a statement, because such a substitution will change the span of ze'ei-cluster.
example of usage:
zo'e bu ze'ei pa
However, in considering the definitions of cmavo using {ze'ei}, I am inclined to make it of selma'o {GOI} rather than {MAI}.
It is because definitions like {iu bu ze'ei ku} are not grammatical. There are many cmavo that cannot stand alone. Those cmavo should be defined with a statement, not with an expanded form of the defined cmavo.
Using {ze'ei} of GOI, the definition of {xo'e} will be:
zo pa ze'ei zo zo'e
mu'o