Changing Up Program Structures?

I have read about how it is good to change up routines so that you keep progressing. But I am still not certain on how often and how much constitutes a change -

For example, recently I’ve been doing full body 4 days in a row and then takign 2-3 days off and repeating (sort of a small cycle of the idea in CW’s 30 day plan). It has worked really well for the last 6 weeks. After the 3 week mark I changed exercises. Does just changing exercises constitute enough of a change or should one also change the on/off structure? Like do I need to change to different pattern than 4 on 2 off?

Same with HF programs - do you cycle HF in and not do it year round to keep it effective, or can it be done all year just with different movements? Thanks!