Magnetization measurements along the easy magnetization direction of a single crystal or textured samples of Y-2(Fe1-xMex)(14)B intermetallic compounds where Me=Co (x = 0-0.3), Mn (x = 0-0.1), or Cr (x = 0-0.1) at an applied magnetic field up to 5 T and temperatures ranging from 4.2 K to T-c were performed. The average magnetic moment values of 3d ion subsystem (Md) inferred from these measurements were interpreted in terms of the itinerant-type magnetism model for 3d ion subsystem in R2T14B type intermetallics and with taking into account spin-polarized-density-state picture for Y2Fe14B found earlier in [1]. A specific feature of the Co-substituted compounds observed from this study is the maximum absence of the M-d(x) dependence at 4.2 K, which is rather unusual for Fe-Co metallic alloys or intermetallic compounds but is in very good agreement with the 3d band structure for Y2Fe14B if the density-state picture for the spin-up and spin-down subbands are not changed upon such substitutions (rigid band model). The M-d(x) calculations based on this approach show that the Fermi level (E) position in R2Fe14B corresponds to the maximal value of M-d and any of its shifting "right" or "left" inside the 3d band causes the M-d to decrease. In addition, introduction of Mn or Cr drastically changes the density-state picture or exchange splitting of the 3d band; thus, both of these reasons yield a sharp M-d(x) fall, which was observed experimentally.