It's not too hard to do, but it's a pain.
The trial doesn't let you save any changes made to scripts, but you can get around it. Basically, all you need to do is create a new project in RMVX Ace. Then, go to the folder in which it is created, go into Data, and copy the Scripts.rvdata2
Create a new RMVX (Not Ace) project. Go into the Game Folder, and then go into Data. Paste the Scripts.rvdata2 into the Data folder, delete Scripts.rvdata, and rename the Scripts.rvdata2 to Scripts.rvdata.
Now, when you go into the VX project and go to the Script Editor, you will see that they are the scripts from RMVX Ace. It will obviously be totally broken if you try to play test, so you'll have to script blind. Once you write your script, save the project. Go back into the Data Folder of the RMVX project. Copy Scripts.rvdata and move it to the Data Folder of the RMVX Ace project. Delete the Scripts.rvdata2 and rename Scripts.rvdata to Scripts.rvdata2. Now playtest the RMVX Ace project. The changed script won't show up in the Script Editor (since you can't shut down without the whole project being deleted), but when you playtest, the script will be interpreted with the rest and so you can test it there.
If that sounds too tedious, then you could also try an
alternative method devised by kal.