probability wheel, redistribution of probabilities
This can be easily achieved by an  array $A$ and an additional variable $m$. The entry $A[i]$ stores the probability of $i$ times $m$.

In your example you start with

A=[1,1,1], m=3


The you increase the probability of the second element by 1/3. This can be carried out by setting $A[2]=4$ and $m=6$, which gives

A=[1,4,1], m=6


In general you could set the probability of element $k$ to $p$ by solving the system
$$\sum_i A[i] = m \text{ and } A[k]=p\cdot m,$$
for the unknowns $A[k]$ and $m$.

So all you need to do is to set $m$ to 
$$ m = \frac{\sum_{i\neq k} A[i]}{1-p},$$
and $A[k]=p\cdot m$ for the new $m$.