How can I make a macro myself?
You'll probably want either:
And is possible to cIall [sic] two macros I have created to affect the same text?
In general, yes. How you'd go about that would depend on a variety of factors, not the least of which are: what kind of "macro" you make (i.e., a widget or a regular macro), how you want to affect the text, and where the text is (e.g., in a variable or in the DOM somewhere).