is there a way to change the Line number heading to different heading? See attached.

What is the reason for wanting to change this ? You could search the dictionary file however there will be many entries for line number, so finding the correct one will be a little hit and miss.

as our isogen reads this as the isometric number I want to look at changing it to iso number and then include line number in custom data fields.

I think the other way around might work better? Adding your Isometric number as custom data. Custom Data can be mapped to the Border Attributes.