Hi Gary
The simplest solution is to input the required words (master’s thesis, doctoral thesis, doctoral dissertation, etc.) in the Thesis Type field. Of course, this will make the references less usable for other referencing styles, as other styles are likely as not to treat theses and dissertations in different ways.
APA itself is pretty complex in the ways it handles different types of print and electronic theses (Publication manual exx. 54-57; APA style guide to electronic references 8-10). This complexity can be accommodated in EndNote by using a range of referencing types (Journal Article [exx. 54, 55], Thesis [exx. 56-57]; Electronic Book [exx. 8-9], and Web Page [ex. 10]) - though, in saying that, we have corrected the APA output style for Electronic book and Web page to better match the published APA style guides.
A final comment is that theses is yet another example of when it would be helpful if EndNote had the ability to apply conditional logic (if … then …) within output styles’ templates.
Cheers,
John