x,y = 123,123
replace = xyz.copy()
replace[y: y + abc_size, x: x + abc_size] = abc
cv2.imshow('replace', replace)

x,y = 123,123
added = xyz.copy()
added[y: y + abc_size, x: x + abc_size] += abc
cv2.imshow('added', added)

background = np.zeros_like(xyz)
x,y = 123,123
background[y: y + abc_size, x: x + abc_size] = abc
add_weighted = cv2.addWeighted(background, .5, xyz, .5, 1)
cv2.imshow('add_weighted', add_weighted)