changing wheel offset = changing vehicle track. Problem?

[Shonky.]

I am looking at some aftermarket wheels.

After a lot of measurement and staring at the car with finger in belly button I have decided I want

19x8.5 et27 and 19x9.5 et40

my question is, is there a problem with changing the vehicle track to get the desired appearance?

I figure standard wheels are et36.5 so I will be:

increasing the front track by (36.5-27) x 2 = 19mm

and

decreasing the rear track by (40-36.5) x 2 = 7mm

What impact will this have on handling?

I understand that an increase on rear track is sometimes done to aid stability, so what is the impact on reducing it slightly, but more important changing the relationship between front and rear track by (19+7) =roughly one inch?