To answer your question.
Also in the case that Variegata di Bologna was a mutation of Victor Emmanuel, a back mutation does not necessarily means that we get Victor Emmanuel. In fact to obtain again Victor Emmanuel (the same genotype-DNA) the back mutation should occur exactly in the same DNA position of the "forwards" mutation. This is statistically very rare. Most often the back mutations occur in a different position. Thus, although the phenotype of the reverted Variegata di Bologna would look like that of Victor Emmanuel, their genotypes would differ. They would not be the same rose!

As for Victor Emmanuel - Variegata di Bologna.
Five mutations of Variegata di Bologna are listed in HMF. They are the commercialized tip of the very large number of the existing mutations of this rose that is very prone to mutate to a red flower variety. I know three unrelated persons who got one in their garden! This clearly shows that Variegata di Bologna has a genetic instability.
Someone in the past, because of a supposed resemblance of mutated Variegata di Bologna with Victor Emmanuel, proposed that this mutation was a reversion (i.e. a back mutation to the original phenotype). The mutation itself was, thus, considered a proof that Variegata di Bologna is a mutation of Victor Emmanuel. As far as I know, this is the only “fact” supporting this idea as no old references referring the lineage of Variegata di Bologna are available, at the present.
While waiting for a DNA analysis, that would solve the mystery, a great contribution could come from a comparative study of side by side Victor Emmanuel and Variegata di Bologna. It would allow to define and “quantify” the similarities and the differences. In fact a mutation normally affects only one or few characteristics of a rose. As, unfortunately, not many Victor Emmanuel are around, a comparison of photos of the two roses could temporary supply for the side by side study. With this aim I posted many photos of the Victor Emmanuel of Roseto Botanico Carla Fineschi.
This is what we can do. Certainly does not help “mixing the hunter with the pray” i.e. loading photos of the mutated Variegata di Bologna in the HMF page of Victor Emmanuel!