Hi Jacob,In a document you can edit symbols as follows:
1) Check Unlock (the button with an open padlock icon - this temporarily disables grouping in the document)
2) Doubleclick on the text label and type in a new value.
3) Uncheck Unlock
It is very important to remember to uncheck Unlock when you're done with your edits. If you work on your document with Unlock checked, symbols can fall apart when you move them. Use Unlock with extreme caution.
You can save your edited symbol by dragging it into the Library List under My Libraries. If needed you can create your own folder structure under My Librarues by rightclicking and selecting New Folder.
Once a symbol is shown under My Libraries you can edit the symbol file by doubleclicking on it. This is the best way to add I/Os. Note that you will find it helpful to set the right Grid settings when editing the symbol file, i.e. 2.5mm for a Block Schematic, and work with Snap to grid On.
I hope this is helpful.