Is it okay to change from 20% to 30% ? When im out just playing around i was thinking of just running 20% and when i go to the track to use 30% . Both are same brand and i always retune (when needed) at the begining of each time out. Got some advise from another person who said I shouldnt be doing this.

Its not a problem as long as you re-tune.
All this talk of re-breaking your engine in is absolute tosh.
You'll be fine

I changed from 20 to 30% with no problems, other than having to re-tune. But I have been told that sometimes you have to "re-shim". I think what is meant by that is you put a shim under the button. I was also told that you'll know if you have to shim it because the motor flat-out won't run.

its not recomended! as your motor will not run to peak performance. pick one and stick with it, even try tostay with same brand too if you can

You mostly would need to add shims if you go above 30%, but it is a good point. Check your engine manual.
For most engines you will be fine below 30% though

The only thing that would affect it is quality of fuel. You can change percentage nitro as often as you want as long as you re-tune.

BS.

Definitly check with your motor manf. specs. I have an RB and just switched to 30% had to add a .01 mm shim. That would the only concern. For the minor difference in price why bother swicthing back and forth and haveing to retune every time you go to the track. I know my change from 20-30 was a big tuneing change compared to the every race day minor tune changes.

I have done it all I did is re shim, re tune but once I went up I just keep using 30% as I do not want to have to keep re shimming and tuning all the time. As soon as I get trough with the last 2 gallons of 20% I have I will be running 30% in all of mine from now on.

why run anything else but 30%?its the best,you can run richer with the same performance.

Agreed. This is simply not true.

I do not buy the theory, that says you cannot switch nitro%.
Aside from wasting time retunning and shimming, I would also think you are going to end up with bad fuel, because you will have to open bottles opposed to one.

I have switched fuel from 20% to 30% in my heli. All I did was retune. It ran great. I have also done the same thing on a boat. It did make the needle really peaky which is a sign the comp is too high. I did not have any shims handy so I switched back, this also did not cause any problems. As for open bottles of fuel.
I used fuel out of a gallon bottle that was half used in my buggy. I had not used this fuel in a year and a half as I had changed brands. I decided to use it during practice to get rid of it. After sitting in a half full bottle for a year and a half it made absolutly no difference at all in how the engine ran. It was exactly the same as when the fuel was new. there are a bunch of myths going around RCU. Changing nitro and 'old fuel' are two common ones.

No kidding.
Sure old fuel can be bad but in reality you will not feel any difference until the fuel sucked up 1% of water. Some guy tested this and posted it on a website.

Be careful with advice from RCU.

If you store fuel properly I have keep it for over 1 ½ years with out a problem. How long do you think fuel sits in some warehouses and hobby shops?