In the (default) ViewTemplate shadow tiddler, find this line:
---------------
<div class='subtitle'>
<span macro='view modifier link'></span>,
<span macro='view modified date'></span>
(<span macro='message views.wikified.createdPrompt'></span>
<span macro='view created date'></span>)
</div>
---------------
In order to hide the dates, remove the SPANs with the macro attributes
"view created" and "view modified", reducing that line to the following:
---------------
<div class='subtitle'>
<span macro='view modifier link'></span>
</div>
---------------
To use a fixed (i.e. not date-dependent) expression, simply add the
respective text (the wrapping SPAN is optional):
---------------
<div class='subtitle'>
<span macro='view modifier link'></span>
<span>Winter Session</span>
</div>
---------------
Of course such a fixed expression probably doesn't make much sense, but
I can't think of an easy way to generate conditional output* there.
You could, however, modify the date format:
---------------
<div class='subtitle'>
<span macro='view modifier link'></span>,
<span macro='view modified date "YYYY-0MM-0DD 0hh:0mm"'></span>
(<span macro='message views.wikified.createdPrompt'></span>
<span macro='view created date "YYYY-0MM-0DD"'></span>)
</div>
---------------
More info on date formats:
http://www.tiddlywiki.org/wiki/Timestamps
HTH.
-- F.
* as in, "if(month == 'December') then write('Winter Session')"
for that you'd probably extend TW's Date.prototype.formatString()