Am I correct that selecting this option results in applying the line "Texture_Max_Load=4096" in fsx.cfg? The problem is that while it's ok as far as performance on my machine concerns, this line is changed to the default value each time I edit FSX option in the sim's menu.
No, it's not. It's changed to default only if you just edited the fsx.cfg by hand.
That's the main advantage of setting it with the Addon Manager, it doesn't just write the fsx.cfg, it also write the correct value in memory and calls the appropriate FSX (undocumented) API call to refresh from the value written in memory. The fsx.cfg is written too, but just to allow the value to be read on the *next* FSX restart.
Even if you play with the Max Texture size slider, you'll see that textures will still be at 4096x4096 (check at KLAX, for example) resolution, something that is not happening if you just edit the fsx.cfg by hand.
There's a free utility that constantly rewrites the fsx.cfg EVERY second, to keep the value in, which is not very good for performance reasons and is not useful to update the value in the current session, and other similar utilities provided with products like REX, simply rewrite the value at each FSX start, but you'll lose it if you play with the FSX Graphic settings menu in any case.
The "Force HD texture" option in the Addon Manager is the only way that *really* force 4096x4096 textures without worrying about touching the graphic settings, and works in real time without needing an FSX restart.
