Is it possible? We can used overloaded functions inside xll files, but can we export them to excel?

Yes and no. For each function the .xll exports to Excel, it must register that function. The registration process tells Excel the name of the function, the number and type of arguments the function takes, the return type, some help info about each argument, and the (possibly overloaded) internal name the function has inside of the .xll. The "external" name which Excel publishes must be unique for a given .xll, so no overloading there. But overloaded functions can definitely be exported, they just need different names inside of Excel.

This and more is in the Excel97SDK available from Microsoft.