It is changing back [reverting] because you are not saving the default template.
MAke the changes then save it in your drwdot template file. If you have not set a custom one up, then click on file new and pick the drawing icon.
Select the rapiddraft option, then your sheet format.[1]
Then select file page setup and select fit to page, orientation, and all those other nice details. Select document setting option.
Saveas drawing as mydrawing.drwdot or what ever name ou chose. There are many reasons to set up custom templates and not overwrite the standard sworks template. Your custom versions should not be in the default directory because you will lose them on upgrades.
[1] If you use preprinted format paper or just no format then you should create a custom format which is mostly empty. Trust me on this on, you will regret it deeply in the future if you do not include a format in your drawing.
Crashj 'drafting 101' Johnson