  The unprecedented phenomenon that a charge density wave (CDW) emerges inside
the antiferromagnetic (AFM) phase indicates an unusual CDW mechanism associated
with magnetism in FeGe. Here, we demonstrate that both the CDW and magnetism of
FeGe can be effectively tuned through post-growth annealing treatments. Instead
of the short-range CDW reported earlier, a long-range CDW order is realized
below 110 K in single crystals annealed at \SI{320}{\degreeCelsius} for over 48
h. The CDW and AFM transition temperatures appear to be inversely correlated
with each other. The entrance of the CDW phase significantly reduces the
critical field of the spin-flop transition, whereas the CDW transition remains
stable against minor variations in magnetic orders such as annealing-induced
magnetic clusters and spin-canting transitions. Single-crystal x-ray
diffraction measurements reveal substantial disorder on the Ge1 site, which is
characterized by displacement of the Ge1 atom from Fe$_3$Ge layer along the $c$
axis and can be reversibly modified by the annealing process. The observed
annealing-tunable CDW and magnetic orders can be well understood in terms of
disorder on the Ge1 site. Our study provides a vital starting point for the
exploration of the unconventional CDW mechanism in FeGe and of kagome materials
in general.
