Adjusting Ingredients for a recipe???

What is the best method for making "minor" changes to a recipe without loosing the primary recipe???
(Such as the local homebrew store being out of a certain hop so to make a substitute for a brew session? This is common for me.)
Or if I decide I just want to try a different yeast for a specific recipe.... Any kind of change I might want to make to a recipe without making it a permanent change or at least keeping a record of the primary recipe????
Thanks

Here is how I manage my recipes, with the help of BeerSmith's 'brew log' function:

I have sub-folders in the 'My Recipes' folder which contain my standard recipes.  When I want to brew one, I highlight the recipe in the folder and click on 'copy to log' on the shortcut ribbon.  This transfers a copy of the recipe into a folder called 'brew log'.  If the folder does not yet exist, BeerSmith will create it the first time you use the function.

I then go to the 'brew log' folder and open the recipe.  From here you can change the recipe as you see fit and it will not affect the standard recipe, only the copy in the 'brew log' folder.  I also use this copy of the recipe to record brew day data and tasting notes. 

Want to use the calendar function in BeerSmith?  Go to 'options' >> 'calendar options' and select to see only those recipes in 'brew log'.  When you give the copy of the recipe stored in 'brew log' a date, it will now appear in the calendar.

When I have completed a brewing season, I make a sub folder in the 'brew log' folder for that year and transfer the brewed recipes, along with their data into that folder.  This way, they still show up on the calendar if I go back to view a history of my brewing activities and are still available to see my recorded results and notes.  It also unclutters the 'brew log' folder so that I don't need to go searching through multiple copies of recipes to find the last one I added.