if im saying this correctly. when you start modelling you get a step by step view of your model inside the tool section so if you mess something up or decide to change it to unified or adaptive skinning create a polymesh it becomes available inside the tools palette you just select it then redraw back on the screen then click EDIT to continue modelling, Also its exactly the same as when you save your work say you close zbrush an reopen you are shown the empty document load up your .ztl of your zsphere`s or whatever you made an you need to redraw the model back on screen with the tool you saved to re-model…
im still pretty new to zbrush but have watched loads of tutorials so i hope ive helped you there.
also want to add to this… when in zsphere mode still an you open the tool you saved as zspheres you can still toggle the preview mesh with A an add more zspheres to your model.