Explain what can happen if you line up the digits incorrectly when you rewrite addition problems.

I'm not exactly sure what you're asking, but here is my explanation:

For horizontal addition it would not change the sum of the numbers as the commutative property would tell us that 
10+9+8=27 is the same as 9+8+10 which also equals 27.

For vertical addition it will affect your solution however.
Proof:
  23          while  23
+32                +32    
55                    343

Depending on how you line up the numbers vertically could affect the solution as you might accidentally treat the numbers in the ten's place as though it were in the hundred's place.