One thing to be aware of is temperature drift. Metal film resistors (most likely that is what you have) are quite stable over long periods of time, at least for most applications, but can have a large enough temperature coefficient that can impact the performance of a system. This means if room or device temperature varies, the gain could change.
You could minimise the effect by keeping the resistor away from hot things like the heatsink for the main transistor/regulator and, if necessary, having a cooling fan in the product.
Though at the end of the day unless you are building a precision product the tolerance is likely fine. A typical worst-case figure is 100ppm/degC worst case which means a 30C rise means a 0.3% additional error. If you have designed the product around a 1% toleranced 18kohm resistor, then adjusted it for a real world 17.5kohm resistor, consider if the additional error is consequential or not to your application.