I recently entered Thailand on a six-month multiple-entry e-visa obtained through the Canadian Embassy online. On the PDF print-out, the visa conditions state that the e-visa is for trips in July (I'm currently stamped in until Sept 21) and December / January. My plans have changed since I submitted my initial application, and now I'm hoping to just do a quick border run in September and return to Thailand. Any advice on options or experiences with similar situations?

Better to do land or air entry? I'm guessing you have to re-show the original PDF visa when re-entering the country, as my stamp does not have all the e-visa info on it.