ramsank,
I am not working at the moment, and I do not have SolidWorks running here, so this is tricky.
You can use a design table to control the configuration of an attached part. Search Google for this.
In Excel, you can concatenate the contents of two, three or more cells. You can name your cells, which I strongly recommend. It makes your equations intelligent and readable.
Somewhere in your design table spreadsheet, you specify size. Let's name the cell "Size".
A column in your design table spreadsheet controls the configuration of attached parts. That cell contains the code [tt]="D="&Size&"mm"[/tt]. If Size is set to 20, the result is "D=20mm".
Most of the crazy stuff I have learned with spreadsheets is the result of me using 3D[ ]CAD.
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JHG