You can edit the Pl**.dat files to set every aerial to 1 or 2 frame lag or something. If you set it to 1, I'd assume the game would just round up the L-Cancel lag to 1 as well.
This spreadsheet is your best friend. It lists the location of a bunch of character attributes, including landing lag for various things.
Back aerial lag is listed at 00F0 on the list. That's really just an offset within the 'attribute region' of the Pl** file.
Attribute Starting Point Offsets
-----------|--------|
Character .| Offset |
-----------|--------|
Bowser ....| 0x3644 |
Capt Falcon| 0x3774 |
Donkey Kong| 0x39B0 |
Dr Mario ..| 0x3540 |
Falco .....| 0x37E4 |
Fox .......| 0x3714 |
G & W .....| 0x3614 |
Ganondorf .| 0x371C |
ICs(Nana) .| 0x1188 |
ICs(Popo) .| 0x32A4 |
Jigglypuff | 0x38BC |
Kirby .....| 0x4CE8 |
Link ......| 0x33FC |
Luigi .....| 0x33A0 |
Mario .....| 0x32D8 |
Marth .....| 0x3744 |
Mewtwo ....| 0x3750 |
Ness ......| 0x34E0 |
Peach .....| 0x3894 |
Pichu .....| 0x3454 |
Pikachu ...| 0x3584 |
Roy .......| 0x389C |
Samus .....| 0x3484 |
Sheik .....| 0x3418 |
Yoshi .....| 0x335C |
Young Link | 0x35A0 |
Zelda .....| 0x37F4 |
C Hand ....| 0x08B8 |
G Bowser ..| 0x34D0 |
M Hand ....| 0x0934 |
Sandbag ...| 0x1464 |
Wireframe-F| 0x2FF4 |
Wireframe-M| 0x31C8 |
---------------------
The vast majority of these attributes are 32 bit floats. You can find an online converter page HERE). For example, 3F800000 is 1. That page is for converting float->decimal, but there's also a link at the bottom for the page to convert decimal->float.
So, if you wanted to get to Bowser's bair, you'd have to add F0 to 3644 in hex. Using a hex calculator, I can see that the bair lag starts at offset 3734. All landing lag attributes are 8 'characters' long in the dat file, or 4 bytes.
Plug in the desired value
here and hit either rounded or not rounded (doesn't matter). Copy the value in the "Hexadecimal" window under the single precision section. That is your new value. Replace the original value in the Pl**.dat file with that one.
For instance, if I wanted Bowser's bair to have 2 frames of lag, I would put 2 into the calculator, and end up replacing the original "3CF5C28F" in his file with the new 40000000. Inject the new dat using GC-Tool or whatever, and the burn/play/whatever. For every aerial to have 1 frame of lag, you would need to repeat this process for every aerial of every character.
BTW, I'd like to note that it can be quite difficult to not shield after L-Cancelling when there's only 1 frame of lag. It's hard to release the GC's L and R triggers that quickly.
