Given weighted complete undirected graph $G=(V,E)$ with $n$ vertices and positive weights. Suppose we find minimum spanning tree $MST(G)$ as $T$.Next we want to decrease weight of $n$ edges in $G$ to $-\infty$. So we create new graph $G'=(V,E')$ that contains only edges that have $-\infty$ edge weights. Finally we compute Minimum spanning tree $T'$ from $T\cup G'$.
My question is, if at the first, decrease spcific edges in $G$ to $-\infty$ and then compute minimum spanning tree $T''$, can we conclude that, edges in $T'$ are the same as $T''$?