Switching to no decay

I thought that, when I switch from optimal decay to no decay, this will take affect from this day but regarding to very different TP, it looks like it recalculates all from the very first activity. How is it then and what is difference between switching to no decay (to different decay method) and recalculation? So if I come to off season period and want to switch to no decay and calculate it from today, how should i do it? Certainly tot like this, because it change method from the very first activity http://baronbiosys.com/xerts-magic-setting/

Did you follow all 6 steps in that article and lock your last valid BT then Save (not Recalculate)?
Your signature should update from that date forward, not today.
If results are not as expected file a support request with support@xertonline.com and they can take a look at your data.

I did follow 6 steps, but there is step to lock last BT after changing decay method. I did it so, than changed method back to see difference and then everything stopped to work so I had to do recalculation. It makes more sense to save last BT first and then change to no decay, as you write, otherwise FS for last BT will be differenent, when all recalculates by different method. I will contact support, thank you