Can I lose grafts or hair follicles 7 days after hair transplant by scratching the scubs carefully with my finger and nails?

In general it is relatively hard to actually pull out the grafts about a week after surgery.  You really need to "dig" deep and hard to pull the grafts out.  Dr. Rassman actually wrote about this and published papers on this subject matter.  I personally have, on one occasion, tried to remove two grafts that a particular patient wanted out (because he thought it was in the wrong place).  After 5 days, it was very difficult to coax the grafts out.You may have pulled out a few grafts unintentionally but in the grand scheme of things, there is not much you can do at this point and it probably will not matter much with respect to your overall results.

More than likely no you cannot pull grafts out by simply scratching but you may wish to be cautious anyway. Be gentle.

It is common to see the hair shaft falling with the scabs  7-8 days after the surgery.On the other hand instead of using your nails prefer your fingers and if you see bleeding stop the massage for a few more days.

Hair shedding is normal & common after hair transplant.When scabs are removed, generally hair attached with them also come out of it. These are just hair shafts and not the hair root.You hair will regrow in coming months.So no worries at all.Please visit & follow your hair restoration surgeon for proper assessment & better management.

and your medical history, age and other variables you are usually ok after 7 days.  The hairs normally shed. 

You need to be careful with the grafts the first ten days after the procedure.  If you rub too hard, you may pull the grafts out with the follicles.  Usually after the tenth day the follicles are settled in and it is safe to wash or take out the scabs using your nails, but just don't force it. 

I wrote an article in a medical journal where I followed patients for 21 days and pulled out a graft and sent it to the pathology lab to find out when the graft that I pulled out, was really gone from the recipient area. Patients cooperated with me in this study. What we learned is that wherever there is a scab present, pulling out the grafts will cause a loss of the graft. If the scab was gone in 5 days, 10 days, 15 days of 21 days, the same lesson was learned. Never pull out or scratch the scalp to remove scabs. In addition to hair loss, such actions can cause infection in the recipient area.