What doubledee said!

To add just a bit more to what doubledee said, when a full scale plane is trimmed, it is trimmed to aerodynamically fly at that airspeed. If power is added and trim is not changed, the additional power makes the plane fly faster than the trimmed speed causing the plane to climb to return to the trimmed speed. Same for a reduction of power, the plane wants to slow down - thus the nose drops to maintain the trimmed speed.

What ever you do, do not raise the trailing edge with shims. This will change the angle of attach of the wing, and the angle of incidence between the wing and horizontal stab. The end result is a reduced angle of incidence increases the stall speed and also increases the glide speed and landing speed. In some situations it could render the plane very difficult to control ending in a re-kit. [:@]

Like was said before, learn to correct for the climbing tendency with the trim. If you change anything, shim the engine to compensate. When you move to a more aerobatic plane there won't be as drastic of a trim change to deal with, but it will help understand what is happening in all regimens of flight.

Hogflyer

Scott, do you have someone helping you learn to fly your plane ?
If so do they think that the climb with added power is excessive ?

Some trainers are designed so that they have a shallow glide slope with the engine at idle.
You fly around the pattern at 1/2 throttle, chop to idle and glide in to land pretty much hands free on the elevator and throttle.
Not a bad characteristic at all for a trainer.

Also if the plane climbs with increased speed this helps you if the plane gets in a nose down attitude, as the speed increases it will pull out of the dive pretty much on its on if you have enough altitude.
Again not a bad characteristic for a trainer.
I have not flown a Hobbistar so I don't know if that description fits or not.

Now for the real question, do you like the self correcting features built into the plane or are they bugging you ?
I personally do not see anything wrong with tweaking the plane to make it fly better, with better meaning to make it fly the way you want it to fly. You should think about all of the various flight characteristics of the plane though before changing anything.

If adding down-thrust will "fix" your climbing with throttle issue the plane will mostly retain its no power glide slope, some of its ability to self correct at 1/2 throttle in a dive will probably be lost, and hitting full power in an aborted landing attempt will most likely be different than it is now, takeoffs will probably be a little harder.

Changing the wing incidence, will change a lot of flying characteristics. This is not a bad thing, but you should think about it.
The closer you get the plane to neutral (no trim change required for throttle setting) it will have less self correction from a dive and you won't be able to just chop the throttle let it glide itself in and then flare just before touchdown, the glide slope for landing will require elevator and throttle management.

Good luck to you.

Adding downthrust will not prevent a model from climbing when you add power if it's trimmed for level flight at less than full throttle. Downthrust just changes how much the nose will move when you change power. Even a Pattern-type airplane that's a neutral as possible will climb when you add throttle if it's trimmed to fly at less than full throttle.

The only way to prevent a climb when you add throttle is to trim the airplane for level flight at full throttle. Just be prepared for a good nose drop when you reduce throttle. This also means that the final approach glide may require significant 'up' elevator to keep it at the proper glide attitude.