Yes... if the CG has been shifted back to where its outside the recommended range for the model... a little weight in the front will cure it.

The reason you can get away with allowing it to drift behind the recommended range on a trainer is... trainers tend to specify a forward CG for added safety. You get the CG further back... the aircraft becomes more aerobatic... but stalls get more likely to result in spins and spin recovery gets harder.

As your flying skil increases... you can experiment wil letting the CG get back as far as 30% MAC on the trainer. (I bet the plan's location of rearmost is 25%...) Some models are still controllable with the CG as far back as 37% MAC... that's about as far as any I have found would be stable enough to safely fly.

I know one RC pilot that could probably handle a plane with CG further back then 37%... but even he wouldn't like it. He balances about everything at 35% (which was quite entertaining when he balanced a flying wing at 35%... the design was unstable further back than 18%... but this guy was good enough to fly it that way.)