[PLP]

Not sure how much difference is OK for ABS, though.

While overall the car will behave fine, speed sensors may become more aggressive (it is only apparent behaviour as they will already be close to their tolerance for difference front/rear).

You can change overall size all around, though.
205/50x17 and 255/40x17 have heights of 636.8 and 635.8 mm respectively.
New rear (45 profile) would be 661.3 mm.
the closest match for front would be 205/55x17 with 657.3 mm (only 4 mm difference - although OEM setup is at 1 mm). Yet this is within thread wear range... so should be fine.

Here is a problem, though.
Despite the tire being "specs" it will have a slightly different size on the rim.
If the rim is wider the tire will sit a bit lower, while if it is narrower, it might push the tire out a bit. Take it with a grain of salt as it is tire and rim dependent...

205 50 17 636.8
205 55 17 657.3
215 55 17 668.3
255 45 17 661.3
255 40 17 635.8
245 45 17 652.3
265 40 17 643.8

Example:
155/70x16 is 623.4 mm

155*70/50+16*25.4=623.4 mm

155*70/100 = 108.5 mm side wall height