Hi @UNKNOWN.DESIGN.LAB ,

1.>>>"Standard" table style has a cell width of 63 meters,

In Standard style it is 63.5 AutoCAD units for drawings based on Metric template (acadiso.dwt) and 2.5 AutoCAD units for drawings based on Imperial template (acad.dwt). So it all depend on how you treat one AutoCAD unit in your drawing

2. >>>>how can i edit the standard table style cell width permanently ?

No way, because cell width (the same way as cell height) is not a part of cell style definition. Cell style definition includes information about fill color, alignment, margins, data type, text appearance, border properties. Furthermore - see # 4

3. >>>>In the properties dialogue box the number of rows and columns is greyed out but the table width and height are editable. Can i "Un-greyout" the rows and columns fields and be able to add/remove rows and columns numerically via the properties dialogue box?

It is "by design" - when you have a table already created in drawing, you cannot change number of rows / columns in it by editing its properties (on Windows side it is the same). You can add rows (columns) via Table Visor (you need to select cell at first):

4. You cannot edit or create Table Styles (collection of Cell Styles) and Cell Styles itself in AutoCAD for Mac, this feature is not available on Mac.