I believe my understanding of the Dorico way means that this isn’t really possible, but I wish I could make a set of sixteenth notes eighths or 32nds without moving the following notes backwards or forwards…
You can definitely do the second one of these; the first is possible under certain conditions.
To turn 16ths into 32nds without moving the following notes, engage Insert mode, add an insert mode stop position on the following note (Shift+Alt/Opt+I), and then change the notes to 32nds. The new 32nds are followed by rests as needed.

By similar logic, you can turn 16ths into 8ths as long as you have a sufficient quantity of rests available after the 16ths (since the time occupied by the longer notes has to come from somewhere). Engage insert mode, add the insert mode stop position, and transform the notes.

Yo you just changed my life! Thanks so much man! I didn’t know about those insert stop positions!
I highly recommend watching the video tutorials on YouTube. Markus Hartman’s comprehensive videos are very detailed for getting started, for example, when switching from Finale to Dorico. Antony Hughes’ YouTube shorts also helped me a lot with the transition, and I still like to watch them while working with Dorico whenever I’ve forgotten how something works.