This MAXScript function will force your current snap mode to always be 2D/2.5D in standard orthographic views like Top, Bottom, Front, etc; it will force the snap mode to change to 3D snaps in perspective and camera views.

This product is also included in  Wall Worm Pro Pack. If you use Wall Worm, you should update WW itself and not use this standalone version.

To install this script when not using WW/WW Pro, copy it to your 3ds Max/scripts/startup folder. 

You can customize this plugin by clicking Customize > Customize User Interface : wallworm.com > Auto Snap Mode.

 When assigned to a Quad menu, there is an extra button to bring up the settings UI to save the default 2D/2.5D mode and to choose whether the tool should run at startup or not.

When Auto Snap Mode is on, you can also manually bring up the config menu with this command in the MAXScript listener:

::WallWormViewPortController.loadSettings()