Can you substitute VSOP brandy for pomace brandy?

depends. but generally yes. pomace brandies generally have a stronger more distinct taste. so if using a vsop brandy the flavour will be milder. but of course slightly different. the question is what you are trying to achieve.. in a tiramisu where one of the traditional spirits added is grappa(a pomace brandy). to substitute will create a different, good for sure, but not traditional result. to summarize they are not same. but they do pair well with similar flavors. things like coffee and chocolate or fruits like apples and pears. pomace brandies that have been aged in barrels (if brown in color) will be even more similar in flavor.