It is not valid to set conditions some time after entering ihraam
Question

I forgot to make a condition when entering ihraam by saying, “If I am prevented (from completing Hajj), then my exiting ihraam will at the point where I am prevented.” I remembered it when I was entering Makkah and I said it then. Is this condition valid?.
Praise be to Allah.That is not valid because the condition should be made when entering ihraam, not after that, 
Shaykh Ibn Baaz was asked about making the condition some time after entering ihraam. He said: 
He may not do that, rather that should be said at the time of entering ihraam. What is meant by entering ihraam is when one forms the intention in one's heart to do so.
Fataawa Ibn Baaz, 17/73.