I don't know why you distinguish beyween solid, liquid and gaseous increases to our planetary mass; they all contribute to our planetary mass equally effectively.

It does however complicate the question. For example, most meteoritic material practically immediately adds solid mass, and accordingly increases both planetary mass and density. However, I do not know whether the rate of loss of our atmosphere into space is greater than our gain of meteoritic material. I suspect that it is.

At the same time, I cannot help wondering whether our rate of gain of gaseous material from the solar wind is not actually greater than our rate of loss of atmosphere to space. If anyone in the forum has firm evidence on the point, I should be interested to hear it.

A decade or 2 ago the consensus was that the earth's mass was increasing primarily due to the arrival of many very small dirty snowball comets/meteor(ites). There is a smaller mass loss due to atmospheric gases being swept away.

If (and I'm not sure what actually occurs) most of this H2O remains in the gaseous phase, then the volume of the earth, if measured at the vaguely/arbitrarily defined boundary of the atmosphere, would increase  with material that is less dense than the existing average density of the earth resulting overall in a lowering of the average density.

Note that to all intents and purposes (besides the esoteric) (google phase diagrams and/or supercritical and/or crystal lattice change) liquids and solids are incompressible so roughly speaking their densities do not change with pressure.

For example water (and liquids are more compressible than solids) in the deepest part of the ocean (1000 times more pressure than at the surface) changes less than 1%.