Hi, is it possible to ungroup or select only some lines (or drawing portions) from a sky130 std cell xschem symbol, so I can reuse in the symbol I'm drawing?

Do not Insert the symbol like you did in the picture, (Using the Insert key or menu Tools->Insert symbol), u*se the

merge

function ('b' key) to load the symbol* instead of placing one instance of it. You can then select by area or you can click objects (lines, circles, rectangles) to select them. Holding down the Shift key allows you to add items to the selection. You can then press 'm' (Move) or 'c' (Copy) to build the new symbol. If you want to be consistent with existing sky130 standard cell gates the output pin should be in last position in the netlist. Check this manual page, section "Changing the pin ordering by altering the object sequence number" to achieve/check this. If you are drawing the schematic the pin ordering is not mandatory, as xschem will always make schematic and symbol consistent.