Remember that the aspect ratio (55, 50, 45 etc.) is a percentage of the width (205, 225, 245, etc. So a 205/55 has a theoretical sidewall thickness of 205mm x .55 = 112.75mm. The 245/45 has 245mm x .45 = 110.25mm Difference of about 2.5mm is pretty small.

However the 245/50 has a 122.5mm sidewall = 10mm gain, more significant

I think I just used my hands and pulled them. You could try a pipe leveraged against the tire, but you must back the fender from the inside or risk dinging the sheetmetal.

I'm going to try this, better than messing with camber. Your mention of backing jogged memory of an old post about using a baseball bat and a flexible sheet of UHMW polyethylene material as low-friction backing to roll up fender lips... I'm guessing same approach with a somewhat thicker but still flexible sheet would work well to reshape the fender arches. But I need such a tiny amount, I'll try the two-handed heave-ho first though, taking care not to visualize creating a nice sharp vertical crease ;¬)
Thanks!