I thought Vanguard lets you exchange mutual funds tax free?
From the side of this Vanguard page:
An exchange between funds within a retirement account is not a taxable event and no tax form is generated. An exchange between different funds in a nonretirement account is a taxable event that will generate a 1099-B, provided that the from fund has a fluctuating value (i.e., not a money market) and the to fund is different from the from fund. Conversions between share classes of the same fund (e.g., Investor shares to Admiral™) are not taxable. Moving from a retirement account to a different account type is generally reportable on a 1099-R. Consult a tax advisor for your specific situation.
Both VFIAX and VTSAX are admiral class, so I think I should be okay?