Yes, you can both use the tools together and/seperate...AND you can add or subtract purposes to a petition at any time.
Once you make the change or adjustment stick with it.
Avoid completely changing your petition from day to day. This will get you nowhere
We should always try to form a well-thought-out plan of action before we get started in order to make sure we have all bases covered...the best we can.
It is not unheard of to begin a working...then on the second or third repetition have the desire or recognize the need to tweak it a bit. It is kind of like adjusting yourself in the driver seat once you are finally on the highway with a few hours of driving ahead of you.
Just stick with it...whatever the changes you make....stick with it and see it through to the finish.
Dedication and repetition are the key words.