  We study the charge and spin transport in two and four terminal graphene
nanoribbons (GNR) decorated with random distribution of magnetic adatoms. The
inclusion of the magnetic adatoms generates only the $z$-component of the spin
polarized conductance via an exchange bias in the absence of Rashba spin-orbit
interaction (SOI), while in presence of Rashba SOI, one is able to create all
the three ($x$, $y$ and $z$) components. This has important consequences for
possible spintronic applications. The charge conductance shows interesting
behaviour near the zero of the Fermi energy. Where in presence of magnetic
adatoms the familiar plateau at $2e^2/h$ vanishes, thereby transforming a
quantum spin Hall insulating phase to an ordinary insulator. The local charge
current and the local spin current provide an intuitive idea on the conductance
features of the system. We found that, the local charge current is independent
of Rashba SOI, while the three components of the local spin currents are
sensitive to Rashba SOI. Moreover the fluctuations of the spin polarized
conductance are found to be useful quantities as they show specific trends,
that is, they enhance with increasing adatom densities. A two terminal GNR
device seems to be better suited for possible spintronic applications.
