Can you extend a #10 bare copper ground with a irreversible crimp? and could you run it through 1" PVC conduit? What codes will back up either way. I know you cant have a splice in a location that you can not access but what if its a irreversible crimp?
You can make that splice in any junction box. You will need to leave the usual amount of spare wire that any junction box splice requires, e.g. 6" beyond the end of conduit and 3" beyond the wall surface.
You cannot make the splice then pull it into conduit to reside in the pipe between junction boxes, unless you are using a splice method specifically UL-listed for that purpose; I expect none exist.
NEC 300.15 Boxes, Conduit Bodies or Fittings - Where Required. Fittings and connectors shall be used only with the specific wiring methods for which they are designed and listed.
Where the wiring method is conduit, tubing, Type AC cable, Type MC cable, Type MI cable, nonmetallic-sheathed cable, or other cables, a box or conduit body shall be installed at each conductor splice point, outlet point, switch point, junction point, termination point, or pull point, unless otherwise permitted in 300.15(A) through (L).