This question already has an answer here:
- Can I delay my turn in D&D 5e? 3 answers
The current question is in some sense a follow-up to the following one:
Can I delay my turn in D&D 5e?
The answer to that question is no. The only means to acting at a different turn in the round than that which was assigned to you via Initiative rolls is the Ready action.
However, what if I decide right at the beginning of the encounter that I want to change the position of my turn permanently? Can I choose to lower my initiative? Is there any other way to achieve a similar effect?