What would be the effect of excess taq polymerase on the PCR?
Costly error.
And yes, it will affect your reaction, since the concentration of Magnesium ions, which are needed as a co-factor by the enzyme, is too low. If you need so much PCR product, you can now adjust the rest of the reagents or you could start over and put this on your personal list of errors. Always check the amount of volume, if it is suspiciously high, check again.

If you decide to proceed and work with a 10x larger volume, make sure that the single PCR reaction is not bigger than 50µl, because the bigger volume also affects how fast the reaction heats up and cools down. If your reaction is too slow to reach 72°C for example, the elongation time might not be long enough to get the full product. If denaturating is too short, your efficiency will drop.