First, let me address this:
3: probably wpm sanitizes the field, preventing html. but u could directly edit your /wp-content/plugins/wp-members//wp-members-tos.php to redirect to your tos page
Don’t ever do that. Any edits to a plugin will be overwritten when you update the plugin. In addition, it can cause other problesm.
https://rocketgeek.com/basics/do-not-modify-plugin-files/
I suppose, anyway, that I should create a custom field, even if I red this is a little tedious task, because you should uninstall the plugin, install it, then set again any single setting (I must say, and I don’t know if this is a known issue, I generally loose some settings even when there are updates)
It sounds like you’re saying you think you need to reinstall the plugin to update this? No, that’s not the case. Creating a custom field is as simple as clicking the “Add Field” button in the Fields tab and adding the field you need.
This plugin does not change existing settings when there are updates. If a change to any core options needs to be implemented in an update, it will always seek to port the existing settings to the new format; but that is a very rare occurrence.
Getting the core question – changing the TOS label. The fact that you can edit the label in the Fields editor was actually unintentionally applied when the core functionality of the Fields tab was rebuilt in 3.1.7. This particular label applies a default primarily because it is handled differently than all the other labels.
In order to change it, you can use the following filter:
https://rocketgeek.com/plugins/wp-members/docs/filter-hooks/wpmem_tos_link_txt/
As for the upcoming 3.2.0 version, the filter will still apply; however, there will also be the ability to simply edit the text in the Fields tab (as you are currently attempting to do). My concern with offering this change in the past was how to deal with the existing installs that may be filtering the text and thus calculating an order of priority on which change should apply. But that’s been resolved and 3.2.0 will allow you to directly edit the label.