Why and how did early editors of Dickinson's poetry change it when they published it?
Because these early editors believed that Dickinson wrote in unconventional ways that would puzzle most readers, they altered her poems before publishing them so that the poems could be easily accessible, read and understood by the widest possible audience. This was especially true of their treatment of Dickinson’s highly unconventional punctuation. Dickinson tended to use many dashes when writing her poems, but her early editors often replaced the dashes with more conventional forms of punctuation, such as commas. Here, for instance, is an example of how the opening stanza of one of Dickinson’s poems was originally written:
I felt a Funeral, in my Brain,
And Mourners to and fro
Kept treading -- treading – till it seemed
That Sense was breaking through --
Here is how this stanza originally appeared in print:
I felt a funeral in my brain,
And mourners, to and fro,
Kept treading, treading, till it seemed
That sense was breaking through.
Notice that in addition to regularizing punctuation, the first editors also regularized the use of capital letters. Most recent editions are careful to present the poems as they were originally written, since most recent editors assume that the original formal features of the poems contribute to the poems’ meanings. So the words you are looking for are unconventional and accessible.