Yes, in the 412 you should theoretically be able to push against the trim while in SAS mode. You get the light because the AFCS reaches its limits rather quickly when you do. I tend to fly the 412 in ATT all the time, because it's required to be in ATT for IMC, & at night it's all IMC to me. I don't push against the trim in either SAS or ATT. I use the interrupt button most of the time, because the coolie hat is so slow in ATT mode. You just can't keep up using the coolie hat alone, at least I can't, unless the air is very smooth.
In the S76, the hat quits working much too quickly. It's very quick, & easy to use, but you have to use the interrupt button fairly often, especially in the roll channel, because you reach the limits of the servos & pushing the hat has no effect. Most S76 pilots I know keep the indicator in the roll position, so they can see when the effectiveness is about to be lost, or more often, verify that that's already happened.