It's not about what can be done, it's about where the ragged edges are, and where the core is. If you put any squiggle in the top of す it will make no sense.

It's not about what can be done, it's about where the ragged edges are, and where the core is. If you put any squiggle in the top of す it will make no sense. But you can do nearly anything you want with the bottom half and it will make sense (like an English 'j'). It's not that the stroke order is sacrosanct - there are indeed a lot of ways to write an 'a' in English. But some of those ways will not be well-read by others. Those regional differences can be really confusing. Ask a french person to write the numbers 1 and 7, and then an American. They are nearly exclusively legible precisely because of their orthographic rules. And yet 'people somehow manage to read'. The hard and fast rules are prescriptive, but once you start writing, you realize that some of that prescription ends up as description. There really are detectable orthographic differences in how stroke order affects (generally, of course) how people write.