Hello,
OK, so you could convert your install.swm to install.wim, simply by using WinReducer Wim Converter also available on the website. So no need to use dism.
At the end of the removing process, WinReducer 8.1 save your changes in install.wim, but it depends if you used the "Save in a wim file" option (in "ISO Creator") and defined a split size in the dedicated field :
If you do not want to activate the split option, leave the field blank (as mentioned)