Greetings Man Flex,
Indeed
"if you use engine anti ice, the N1 will increase and you will be above your profile by around 1000 feet on the A319."
Remember AIRBUS doesnot want Anti ice function to cater profile change (Boeing Does have a function) and AIRBUS did not embed ANTI ICE or Speed Barkesin the Profile.
Descent:
The aircraft will descent at IDLE + delta (i.e., Speed on Elevator) until it reaches the first constraining constraint then continue geometric descent (i.e Speed on N1)
Now the only way to fly IDLE all the way is to clear all constraints present in the fms on the descent segments and up a constraining contraint at XXXX feet. Is it safe
well no
some constraint are linked to terrain profile airspace and traffic
