You can open an existing macro file by navigating to Plugins | Macros | Edit... You can then do all the modifications you need (for instance, you can restart the recorder and add more commands if you need them, or comment what you did previously), and save the file again.

Note that the macro commands store the parameters used for each tool. Suppose you want to change some of them (for example, setting a rolling ball radius in the background subtraction tool of 40 instead of 30). In that case, you only need to edit the macro file and substitute:

run("Subtract Background...", "rolling=30");

By the following code:

run("Subtract Background...", "rolling=40");

Then you can rerun the macro and see the difference in the results.