I don’t know if this is intended behavior or not, so I thought I’d post it and let the Beeniuses sort that out.
I recently started a goal to track words edited on a specific project. Today I decided to track pages edited instead, so I scaled the goal by 0.00266666… to convert from words to pages. That went fine. (And it updated my commitment to use “page units,” as hoped, so: awesome!)
Then I decided I needed to up the daily commitment from my originally modest goal. So I went to the road editor and changed the very first line from 12.5… to 35. I mean, why not play around with the massive power at my fingertips? Why not see what happens? (Chelsea and Bethany groan in unison)
Beeminder flashed a red “Resource not found” banner at me. Totally cool; I didn’t think I was allowed to change the rate within my akrasia horizon. I refreshed the page, intending to get the old road editor values back in (because of the elsewhere-mentioned state display update issue, it was still showing me the 35 I’d entered). And… it updated my road from day one, as I’d wanted to do.
So, hey, cool. But is that intended behavior? Was it OK because I was increasing the difficulty of my commitment? If I’d tried to change from 12.5 to 2 within the akrasia horizon, would it have stopped me?
My first attempt to reproduce this wasn’t successful (changed the first full row of the editor to something harder) but to answer your question, yes, if you try to decrease the rate within the akrasia horizon it should stop you. Feel free to test that out! (Bethany and Chelsea again groan in unison).
I think that increasing difficulty was supposed to be allowed even within the akrasia horizon.
However, I would like to confirm that I have also encountered some odd error messages when changing things in the road editor - and the result saved regardless of the error message.
Increasing difficulty within the akrasia horizon is allowed - sorry, what I wrote was a bit unclear. Decreasing the rate in this case means decreasing the difficulty, which wouldn’t be allowed, but increasing the rate and therefore increasing the difficulty is allowed.
Interesting—because I could swear all my changes on the old design, harder or easier, only took effect from the akrasia horizon forward. In fact, I counted on that, knowing that if I made a goal harder I still had a week at the old rate to get my butt in gear.
So my first question is: is this only true for heavy-hitter Bee Plussers and up, who now have the massive power of the road editor? (cue clashing cymbals and gongs) Or is it also true for people on the Free and Infinibee plans? 
Or is this something that recently changed, with the new design?
In any case, it’s probably worth making the behavior crystal clear in the Super Helpful Beeminder User Guide in Plain Language. (Which I believe @drtall was going to write? ) In all seriousness, I think a one-stop user manual would be a very good thing to create. If well done, I’m pretty sure it would cut down on support requests and reduce the number of newbees who freak and bail.
 I went from Infinibee to Bee Plus this week, so that could explain my confusion if it’s a Bee Plus (plus) thing.
Yep, it’s not an old design vs new thing, but rather a road editor vs normal road dial thing. It’s mainly to simplify things - it’s (relatively) simple to understand “all changes take effect in a week”. Enjoy your newfound power wisely.