The term "work session" is not covered by public meetings laws, which recognize two kinds of meetings: regular and special. The term work session has become popular to indicate a meeting at which the board does not intend to take any action. You have to post the work session as a regular or special meeting. (The former would go on the calendar you set in July; the latter would not be on the calendar you set in July).
Legally, the board is authorized to do whatever it does at other regular or special meetings.
Your community, however, may have expectations about a meeting described as a work session. If you have developed the expectation that no action will be taken at a work session and, out of the blue, you make an important or controversial decision at one, the community may be very upset, even if you haven't broken the law.