Yes, you surely can. Create a calculated field for each of such dimension, using IF or CASE condition.
Like IF [A]="True" THEN "Yes" ELSE "No" END
or CASE [A] WHEN "True" THEN "Yes" WHEN "False" THEN "No" END
You can post a packaged workbook, if this doesn't work out.
Thanks. I thought this might be the answer unfortunately. I have something like 50 dimensions and was hoping for something that would affect them all at once.
The easiest way would be to replace them in the excel sheet itself, using Find and Replace All. This way you prep the data for easier handling in Tableau.
Manipulating 50 odd dimensions can become a tedious task in Tableau.
As Manas said, you can't affect them all at once in Tableau, so you might want to do data prep.
Alternatively, instead of calculated fields, you can assign an Alias to True/False so that they are Yes/No.
If you do this in the data connection window, you can save this data source so that you only have to do it once, but the data in the back end can change without having to do the prep work.