The short answer is "it depends". Running it on the lower frequency means it will run 20% slower therefore and because V/f ratio has changed from 110/60 to 110/50 current is 20% higher so it will run hotter. Whether that is an issue I can't say because it depends on how its used. Short bursts of use with time to cool down might be a practical solution. An alternative approach is to bring V/f back in line by using a 240/90 step down rather than 240/110. This will bring current back in line but will reduce power by 20% (power = revs x torque, and torque is proportional to current) so you may have to reduce feed rates and/or DOC.