Let's say I make an adsense code for 336X280 format then I put it in notepad, so when I have a new blog I only need to paste the code into my new blogs. Is this allowed?
NO that is not a violation. However I dont reccomend that you do it. Why? Because AdSense has channels that you can set up and use to keep track of where you are getting impressions and clicks. Being able to see those stats is very helpful to a webmaster. If you use the same code for all your sites you will not be able to know whch sites are getting clicks and how much they are earning for you.
how about if i use my adsense code from one blog to another blog, is it allowed? meaning to reuse the same set of code in different blogs at different times, not concurrently?
The answer to that is the same as what I posted above. It would not violate the TOS, but it would put you at a disadvantage as far as your stats and tracking goes.
kentuckyslone pretty much got this one. It's also wise to try different size and types of ads as well. Using the channels you can track each of the ads and determine what works best for you. If you havn't already, I recommend installing google analytics on websites its a good compliment to any stat tracker you have.