Efficiency Calculations in beersmith

Hi All
First I apologize for this question as I saw many threads about it (I learned from them how to calculate) but still I have one major question remains.
As I understand (i maybe wrong) the ingredients bill can change according to my equipment efficiency right?
And to calculate the efficiency (Mash) I need to actually perform the Mash but if the efficiency is not as in the recipe I need to change the ingredients to hit the OG target but I get this after I already Mashed, so I really don't understand it, Unless you will tell me i need to "sacrifice" this batch (will be different from recipe not ruined).
Thanks and sorry again.

As you start doing all grain batches you won't know how efficient your process is so you make some assumptions and base your ingredients on that. A good start would be to assume 65-70% as that is withing the normal range. Make your batch but make sure you have some malt extract available in case your efficiency is lower so you can add more fermentables. If your efficiency is higher than estimated, you'll have to just suffer through beer with more alcohol than expected. Once you have done a few batches you can change the estimated efficiency to closer reflect what you typically get.

Thanks a lot RM-MN, yes I will have some extract that is a good idea the alcohol issue I can certainly deal with (-: