Rewiring in metal conduit
Don't replace metal pipe with PVC "just because it's what everyone uses today". Metal pipe is superior in every way.  And may also provide a valid earthing path.  

You should not use cable in conduit.  You should use individual wires which are rated for pulling through conduit.  For instance, North America uses THHN, which has a nylon outer coating to make it slick for pulling. Surely any wires sold as individual wires will be made for this, because it will obviously be used in conduit! 

All curves in your conduit should be broad turns.  If you have sharp corners, there will be a removable cover to access the wires.  You do not drag wires around corners -  you remove the cover, pull to there, then pull the next segment.