How damaging is freezing CB assets?

Not much. Just that the CB is not able to manipulate currency markets

A new level of economic and financial restrictions have been imposed on Russia after the invasion of Ukraine. One element of this is the freezing of central bank (CB) assets. The adverse impact upon the CB, from freezing assets, is less extreme than is commonly supposed. It remains possible for the CB to construct the ruble and to do inflation-targeting, it just interferes with the ability of the CB to influence the market price of the exchange rate.

When China initiated hostilities against India, they argued that economic activities should continue unhindered, while soldiers kill each other at the border. This