What happens if I temporarily change my plan?

If you subscribed before the 12 you should be correct

For members who subscribed BEFORE April 12, 2019.

If your plan was activated before April 12, it will return to its launch (introductory) price once the stabilization period is over. Please note, however, that if you change your plan after the stabilization period, regular prices will apply. You will be notified of the end of the stabilization period one month in advance.

Since you subscribed before April 12, you will get to keep the Introductory price for whatever plan you are on at the end of the stabilization period.

I believe you are free to make changes to your plan during the stabilization period and as long as you activated before April12th you will get to keep the Introductory pricing of that plan (with whatever changes you made) when the stabilization period ends.