Is there any disadvantage to changing trace width in the middle of a trace?
Yes, but these disadvantages may be negligible.

Disadvantage 1: High frequency signals encounter a discontinuity.

I would start worrying at a few hundred megahertz because the change in trace width changes the characteristic impedance (not just dc resistance) of that line. The discontinuity changes scattering parameters, creates harmonics, reflections, and other headache-inducing problems.

Disadvantage 2: Voltage drop (and increased power dissipation) due to higher trace resistance.

If the decreased-width percent of the trace is less than 10%, I wouldn't worry. All of these effects can be calculated for your potential design, however.

Here's an online tool that helps estimate trace resistance

Here's a downloadable tool that has a lot of built-in equations