You're not going to lose
'that' much fuel anyway, so it makes no difference what level the fuel gauge is at. The only thing I can think of is maybe Haynes think a full tank will have more pressure, which would make the filter housing harder to get off. However, there won't be pressure because the engine won't be running when you're doing this job & therefore no relays/pumps are working.
I know when I changed my fuel filter that I didn't look to see what the fuel gauge was showing & it didn't make a bit of difference to the job in hand. Get it changed
