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TTL was designed for 5 V only.
The internal organization of the SN7414 is not documented. But let's look at the SN7404:
When you change VCC, the currents through all the resistors will be different. For the SN7404, this means that the input currents, output currents, and timing characteristics will change, and are very likely to go outside the guaranteed electrical characteristics.
The SN7414's inputs have Schmitt-trigger circuits. When you change VCC, the resulting changes in the various biasing voltages might not only change the characteristics for the worse, but make it fail altogether.
If you really want to use the SN7414 in your circuit, you have to test it yourself: find out at what VCC the device actually fails (over the expected temperature range), and then stay far away from that.