Hi there,

so to continue to have Roll Over Data you will definitely have to choose this perk on your new plan, but if you change the plan the amount the collected data will be gone as it is dependent on the previous plan not the perk.  Keep in mind if you switch the plan you will be given a prorated amount of data until your next billing cycle, so you won’t actually have the full amount until your next bill cycle again as well. For more information on this check out this link: https://www.koodomobile.com/en/help/koodos-pick-your-perk-plans?search_api_views_article_search_fulltext=undefined

Your rollover data doesn't actually accumulate over months - the following is from Koodo:
 

Any data leftover from your plan's data bucket in the current month will get added to your data bucket for next month. Your Rollover Data will get used automatically after you use all of your regular plan data. You can only keep your Rollover Data for one month, so any unused Rollover Data at the end of the month will expire.
Note: Once the data included in your plan has been used, you’ll start using your rolled over data automatically.