Would hopefully be helpful for folks that wish to tailor this mode as well.

One of the most glaring issue with the base game's control is that you can't unequip a hotkeyed item using the same hotkey. So I started off with the idea of swapping 2 pieces of worn equipment, but hot-keyed. 1 with the bullet time effect, the other without.

Initial version started off as a Power Armor mod for the left arm (coz I can then fluff it as an interface to the Pipboy). And drains fusion core instead of AP.

Now, I also wear charisma boosting items and when I need to speak to an NPC for speech checks, I will exit power armor.

After playing with this for a week, 1 shortcoming of my design became obvious, I kept having to re-hotkey the armpiece that was left in my powerarmor after I exited it.

If I attach the effect to normal clothes, entering power armor would disable their effects.
I wasn't about to make 1 set of triggers when I am in PA, and a 2nd set when I'm out.
So, what doesn't get un-hotkeyed... the answer I arrived at was... Weapons.

I can attach effects to weapons, but it works differently from armor. Weapon effects are applied to the target you hit. They don't apply to the player equipping the weapon. Dangit...

So what else works both in and out of power armor? Answer finally came to me after a few days - Perks. After looking at the existing perks, it turns out that activation of perk effects can be tied to conditions. Hell yeah! I'll just add a condition for bullet time to activate when I am equipped to whatever triggers I choose.

Armor and clothing was a second choice, since I want to avoid spending an apparel slot on this. Started looking at weapon slots. Woot! Another treasure trove of equipment slots that can be used!

Grenade slot and arm slots tend to interfere with weapons and grenades. but slots like Others, PowerArmorBattery, shield and potion seems safe to use. "Shout" slot are sometimes used for other stuff, so I avoided using it.

I didn't want to add perks by using the console, so the logical solution is perk magazine. Findings for that -
The swf animation determines how long the sound is played. If sound file takes 4 secs and animation takes only 3 secs, the sound being played will be truncated after playing for 3 secs. It will keep looping as well, so if there's no break in the sound file, it gets a bit annoying.

Swf files are a pain to edit as well. Images have to be exported 1 by 1. The images are of different sizes. One lesson learned is that I need to keep the image size the same. I increased the size of some of the pics and after importing it back it, the swf file will shrink it to fit the original defined offsets.

Perk magazines can be created. But will crash because it immediately brings up the special magazine interface, which interferes with the crafting screen.

Finally, I have alternate version that use slow time effect rather than the slow time jet effect, but without the sound and visual effects, looks much better, but it's a bit hard to tell if the effect is up.