Hi Dave,I'm assuming you've saved the symbols you created into your Library List under My Symbols.
You can edit a symbol file by doubleclicking on it in the Library List. Click on YES when asked if you really want to edit it.
When the file opens I'd recommend first setting the grid size to be the same as the Block Schematic environment. Rightclick, select document and go to the Grid tab. X and Y grid spacing should be 2.5mm. You can then copy existing ports, edit labels by doubleclicking on the text etc. and perform any other drawing/editing action you want. When finished, just save and close the file.
The same is true for any rack symbols you have created, but note that the grid should be X=25.4mm, Y= 44.45mm.
I hope this is helpful.