Try setting the file to read only. It might work, but most programs can change attributes of files, these days.
I almost think it is a very clever marketing tool to get people to download the plane because they think they can get it for free. 😂 Would they have generated as much buzz about their products if some folks didn't think they could get it for free,
If you really want to defeat their protection, try this.
1. Edit the file.
2. Copy it to a different name.
3. Create a batch file that copies the renamed file to their file name.
4. Put the batch file in your startup folder so it works every thime you start your computer.
If the model keeps working after the expiration date, you've been successful and the software devlopers will learn they need to put a bit more effort into protecting their products. If not, you will learn that it is easier to purchase the product than waste all that time trying to get something for nothing. 😂