1. my target school has average gmat of 680. I will be sending my score before exam since 5 are free. so incase I send score to xyz school for r1 with a 600, can I retake and send the new score lets say 700 in d same school in r2?
yes you can do that, as long as you provide them with the improved GMAT score.. the thing is when you request GMAC to send you GMAT score to the school you are applying, they send the your entire history in GMAT. Schools typically only consider the last score ( or the best score in some a cases if the test was taken within a certain years before the application date. )
2. incase I apply to xyz school in r1 but dint get an admit...can I apply with gre score in the same school for mba?
You can't apply in the same year.. As a student you can apply only once a year.. you can try the next year with a different score.