The Label field is not a “multi-text” field, so any imported text will appear as it is formatted in the tagged file. There isn’t a way currently that you can separate this data with returns. If the data had been presented with returns or if the terms were all prefixed with their own tags, then you would have the return between each one. The Keyword and Author fields are the only true “multi-text” fields currently available with parsing commands for each.
One way to separate these terms is to create a new “Terms” list (Tools/Define Terms Lists) If you create a new list, then use the semi-colon as the delimeter and then “Link” the “Label” field to the list, each time you import the terms will appear as individual terms in your new terms list. This makes it easier for you to search or use these terms for subject bibliographies or to separate references into their own categories.
One way to handle this, if you wanted then per line, would import it and then edit the Label field globally in Endnote to replace the ;<followed by a space> with a carriage return (special character drop down). this is thru the File, find and replace command.
You would obviously have to do this every time you did an import though.