Shift Button

You can designate one cabinet button as the local Shift button. This isn't related to your PC keyboard - it's not that Shift key. But it's a similar concept: it lets you give every physical button on your cabinet a second key assignment that you select by holding down the local Shift button and pressing the other button.
This is great if you want to minimize the button clutter on your cabinet, since it lets you double the number of PC commands you can access with your existing buttons.
To set up a Shift button, enter the button number that you want to use as the Shift, or just click on the shift icon () in the button's row in the table.
Once a shift button is assigned, every button in the table will let you enter two key assignments: a regular key assignment and a shifted key assignment. The regular key is sent to the PC when you press the button without pressing the Shift button. The shifted key is sent when you press the button while holding down the Shift button.

Mode options

The Shift button itself can have a regular key assignment, just like any other button. (It can't have a shifted key assignment, for obvious reasons.)
The handling of the Shift button's key assignment is a little tricky. It involves some trade-offs, so the controller lets you decide which way you want to handle it with the Shift button mode setting.
Shift OR Key mode: This is the default. In this mode, the Shift button serves only one of its two functions on each press: it's either the Shift button, or it's an ordinary button with a key assignment. Which one it is depends entirely on whether or not you press another key while the Shift button is pressed.
To make this work, the Shift button can't send its assigned key assigned key to the PC immediately when you press it, the way a normal button would. Instead, it has to wait to see if you're going to press another key while the Shift button is down. Here's how it decides what to do next: This mode is the default because it lets you safely use any button as the Shift button without any unwanted side effects. For example, suppose you assigned the "Exit" button as the Shift button. Normally, pressing this button terminates the current pinball table and returns to the selection menu. When you use Exit as a Shift, though, you probably don't want that to happen. It would be annoying if you just wanted to adjust the audio volume, say, and it also exited the game. The "Shift OR Key" mode avoids unwanted side effects like this by skipping the regular key mapping every time the Shift function is used. The tradeoff is that the normal key press is delayed until you release the button.
Shift AND Key mode: In this mode, the button sends its ordinary key mapping on every press, in addition to its Shift function. Since the key is always sent, there's no need in this mode to wait to see if you're going to press another button. This lets the controller send the mapped key immediately when you press the button, just like for any other button.
This mode eliminates the delay in sending the key that you get in the "Shift OR Key" mode - the way the key isn't sent until you release the button rather than when you first press the button. Some people find that delay confusing or just annoying. If you don't like the delay, this mode lets you get rid of it.
The tradeoff is that the button can't be "smart" about whether or not to send its mapped key on each press. It just sends it every time. So if you use this mode, just be careful to select a button that won't have unwanted side effects when it sends its mapped key.