Your code works for me, with one modification - using Vals.Value instead of Vals.Values.
One thing to be aware of, Your code works in this example because all the values are less than 50. The conditional statement in an if statement accepts a single logical outcome. When you use a logical comparison on a vector, you get a result for each comparison. Therefore, the if statement treats it as if it were written all(Vals.Value <= 50). If every coparison is true, then only the if statement code runs. If even one is false, the only the else statement code runs. Either way, only one condition is executing.
The solution is to either use a for loop to check each value one at a time, or better, use logical indexing.
ind50 = Vals.Values <= 50;
Vals.Values(ind50) = Vals.Values(ind50) + 50;
Vals.Values(~ind50) = Vals.Values(~ind50) - 50;