Thanks Jerry, great ideas.
I will try the delayed single write and report what happens.
My objective is to have a software ALC or power limiter for SSB (and mainly for digital modes) where I can control the output power. Since I measure the forward power continuously my thinking is to use the slope of the first IF filter like I do with the software AGC.
In Rx there is a very slight "pop" when the increase of both clock 1 and 2 occurs (see Ian's Youtube video) and I suspect this is related to the time difference between the changes.
The effect is barely noticeable, but in TX I may for a millisecond or so transmit on a frequency 4 or 6 khz away from the current one. Since I don't think that is good practice I am researching how to avoid it.
Worse case scenario I will disable the clocks, change frequency then re-enable them as you mentioned.
Hope that makes sense.
Thanks and 73, John (VK2ETA)