Использование простой итерации & enumerate
Ex:
lst = [[(7261, 8764), (7288, 8764)], [(4421, 8937), (4448, 8937)]]
result = []
for i in lst:
temp = []
for ind, (x,y) in enumerate(i):
if ind == 0:
temp.append((x+7, y))
else:
temp.append((x-7, y))
result.append(temp)
print(result)
Выход:
[[(7268, 8764), (7281, 8764)], [(4428, 8937), (4441, 8937)]]