Hi Lou,
thanks for your reply.
This still doesn't allow me to change multiple fits in one go though, does it? I can't select more than one entry in the Customizations dialogue, so that when I have, say, 15 fits, I can change the line width of seven of them in one go. I still have to do it separately for each fit.
I like the approach with copy/past customizations (this would have been my next question, how do I transfer formatting from one plot to the next), however, I can't get it to work. When I've changed, line widths, colours, and line style in one plot, clicking "Edit -> Copy Customizations" in it and then "Edit -> Paste Customizations" in the target plot does not seem to have an effect.