Having a look on real time trains the train from Gatley arrives into platform 9 and the train to Euston into platform 8 so it might be possible to make a tight connection since they can arrive into the platforms adjacent to each other.
It will almost certainly not affect the viability of the connection. The train is usually 3-4 minutes early anyway given the time of the morning - but this means I can no longer get an Advance ticket on the 0635. Or, I could book an Advance on the 0635 from Manchester but as it's not an official connection if the train from the Airport line were late for any reason I might potentially have to buy a new ticket. To ad insult to injury, as far as I can see the train has retained the same timings throughout except for taking an extra minute to do Mauldeth Road to Piccadilly. Note that Heald Green passengers are unaffected because there is an Edinbrugh train that stops there just before this one.