Welcome aboard to Pattern!!

I just started to fly Intermediate at the end of last season after skipping nearly two years.

I always try to keep the speed constant and was taught to do so for smoothness.

In my case, the plane is a little heavy in overall, so I use full throttle during vertical up and reduce the throttle during down.

If you keep the throttle at the same level during a loop, going up is fine, but the plane will increase speed when it come down and also will be sensitive on elevator compared to up flight.

As long as your manuevers are done smooth & round at near constant speed, you won't have problem, but I would recommend to throttle down on downside.

When fly loop, I do following way of throttle.
Level flight is mostly half throttle, when entering the loop, I start to increast throttle smooth so that the plane does not suddenly change its speed.

When the plane is up at the top of the loop I cut the throttle to keep it's speed.

After passing 3/4 of loop, I begin to add throttle back to half throttle exiting to level flight.

This is just my case with one of my plane.
In your case, your throttle setting will be different since you stated that the plane will do manuevers at half throttle.

How large are your manuevers?
I tend to make manuevers too large for my plane, doing this actually show all those mistakes during manuever.

If you make a manuever large, be sure that you will stay in box.
Also, do not make those manuevers too small, if this becomes your habit, you will have hard time adjusting and flying a larger size plane later.

Try to have a coach (pattern pilot who knows the manuevers described in the judging guide) if you don't.

I don't have a coach anymore. I am the only pattern guy in my area, so I have to practice a lot more and ask my friends at the field to look throught my manuevers and tell me how they were done. It still helps a lot.

Also, I don't understand exactly what you mean by "reset the trim".
If you are talking about the trims on each control surfaces, you need to find out the correct trim setting.
Most of our planes do not need trim changes once set correctly.

Try check out the trim-sheet at NSRCA. CG is always the most important thing, so it takes a while to setup a plane correctly.

http://nsrca.org

All you need is practice.
It shows at contests if you had lots of practice with correctly trimmed plane.

Hope this helps,

Sorry for the long post. I tend to go long most of time when I try to explain something.