Is it permissible to combine the intention of making up two missed fasts from the previous Ramadan with the intention of fasting Tasu'a and Ashura for blessing?

If the questioner intends by "the intention of blessing" that the fast coincides with a blessed day or the blessing of the fast itself, without intending the Sunnah (definition) of fasting the ninth and tenth of Muharram, then there is no harm in combining the intention of making up a fast and the intention of blessing. However, if she intends by "the intention of blessing" the Sunnah of fasting the ninth and tenth of Muharram, then this is not valid because it involves sharing the intention between two independent acts of worship.