Is it possible to do an alternate Guard Impact

Guard impacts are performed with the combination ◁A+B+K (4A+B+K) and takes half of a soul gauge meter, regardless of whether or not they hit.

Additionally, certain characters have combinations that perform a guard impact. For example, Siegfried's B+K stance transition includes a guard impact. You'll be able to recognize these by their green glow as the animation occurs.

The trick to doing just guard

To do the just guard, you have to press and let go of the guard button (for a total press of four frames or less) while your opponent is mid swing. You have to have already let go of the button before the attack connects to activate just guard. You have to let go of guard roughly 0.25 seconds before the hit connects.

The best way I've found to practice

Go to training and select a fairly slow character like Nightmare or Astaroth as your opponent. Set the CPU to counter after attack. The computer will automatically attack after each time you do. It's pretty easy to nail down the exact timing when you initiate it with your own attack. Attack, just guard, attack, just guard. After a while you'll be getting it on every try.

Practical timing in a live match

The three scenarios I've found the easiest to time against real opponents are:

1. Immediately after a guard. Many less experienced players will counterattack as soon as they're done blocking. If you practice using the method described above, it should be pretty easy to time when that counterattack is coming.

2. The last hit of an obvious combo. Most characters in the game have their trademark combos that a large portion of players use (usually B, B). Getting the timing between these two hits down is relatively easy. Guard the first hit and use just guard on the second. The timing should come naturally after some practice.

3. Unblockables. Probably the hardest of these three to time, but totally worth it if the people you play against favor using these. Unblockables are generally slow, so you have a second or two to prepare yourself and get the timing just right.