Applications of single-walled carbon nanotubes (SWCNTs) require the nanotube samples with uniform properties. The filling of SWCNTs is a promising method of tailoring their properties. Other way to obtain the samples with homogeneous properties is to perform the separation of filled nanotubes by conductivity type. In this work, we performed the sorting of nickelocene-filled SWCNTs by density gradient centrifugation to metallic and semiconducting fractions. The obtained samples were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy. The investigation showed that the samples have homogenous properties, high quality and high purity. The encapsulated nickelocene has n-doping effect on metallic and semiconducting SWCNTs. The samples were annealed in vacuum at 360-1200°C to grow inner tubes inside SWCNTs, and the electronic properties of these samples were investigated. The annealing of nickelocene-filled SWCNTs leads to decomposition of molecules with the formation of nickel carbides and pure nickel inside double-walled carbon nanotubes (DWCNTs). It was shown that annealing of nickelocene-filled SWCNTs at 360-600°C leads to n-doping of SWCNTs, whereas annealing at 800-1200°C results in p-doping of SWCNTs.