you can use WM to add a third limit to levels 1-2 for everyone except tifa, cait, and vincent. So you could stay at level 3 and have their normal level 4 limit be learnable by either a certain number of uses or kills. But you cannot force it to be learned by the item so it would be entirely possible to obtain omnislash in the first reactor with this method.
The most fluent way to get what you want would be to just add the first limit of the next level to the bottom of the list.
so for cloud it would look like
braver
crossslash
blade beam
blade beam
climhazard
meteorrain
Meteorrain
finishing touch
omnislash
Omnislash.
You can also rearrage when the character obtains the limits and you can even adjust some things like base damage and effects caused by using a program called Libre, but its very finniky and the only time i tried I failed to make it work.
Level 4 only has 1 working limit slot and is hard coded to be learned by the characters specific item so its impossible to add with our current tool set (sister ray will probably change this) Vincent, cait, and tifas effects are pulled based on the limit level selected so you cant edit them around or give them extra limits ( you can give cait an extra limit in level 1 but its janky at best)