You can download Google Fit and link MyFitnessPal to Google Fit. Then you have to install Health Sync to synchronise from Google Fit to Samsung Health.
I am not sure about the editing part but I use Health Sync for syncing and importing data. I also paid for the full price for historical syncing. It works fine. Does this work for you?
You can link Fitbit or Google Fit to Samsung Health with the 'Health Sync' app (https://play.google.com/store/apps/details?id=nl.appyhapps.healthsync). So you can also link apps to Google Fit for example Heart Rate Monitor, then Google Fit send it to Health Sync and Health Sync send it to Samsung Health so that you're heart rate is visible in the Samsung Health app.
A lot of things have integration with Google Fit but not Samsung Health. That said, I use Health Sync to sync all my Samsung Health data to GFit, and have other apps pull info from there if they don't have direct access to Samsung Health. There are other options for sources and destinations too, if you'd find those more useful. You can get it here: https://play.google.com/store/apps/details?id=nl.appyhapps.healthsync
I used Fit and Healthy. You have to pay for all of its features. And I was only able to sync my last 30 days of steps. Everything else seemed to sync.
It's not perfect but better than nothing.
https://play.google.com/store/apps/details?id=com.jsonlo.fitandhealthy
I was struggling to sync mfp into SHealth, but somehow it worked after trial and error.
First, disconnect each other (in mfp first and then deny all permissions in SHealth, if any). Then, connect each other but give only steps and exercise permissions. Clear both apps' cache and sync. Then give write permissions for food info and food intake. Leave it for 5 min, sync and clear apps' cache. Open mfp and then SHealth and sync. Finally give read permissions you gave for write ones as above. It may starts sync after a half an hour. Once it gets synced, you don't have to worry about it anymore.
As for the "other workout", yeah, you choose the closest one with the exercise you done. I suppose each exercise has a different calorie calculation. But in general, it is mostly an exercise diary with no other use other than suggesting you how much you should exercise with each workout in order to achieve your calorie goal
Tip: You may use apps for workouts that sync to Google Fit. Then you can sync Google fit workouts to SHealth using the Android app "Health Sync" https://play.google.com/store/apps/details?id=nl.appyhapps.healthsync 7 days trial. It costs around 4 bucks (or 0,70 cents/month subscription).