Just to get several things clear:
Action groups can be accessed via the actions menu, the toolbar buttons or right-click on selected items in the filelist.
Tools can be accessed via keyboard shortcut Ctrl-0 to Ctrl-9 or right-click on selected items in the filelist.
Action groups execute the stored actions which are MP3tag internal commands and completely under the control of MP3tag.
Tools execute external programs which are not under the control of MP3tag.
A mixture of actions and tools is not possible but have to be called separately.
It is good practice to have tools for file manipulations that are outside MP3tag's scope, e.g. treating the audio part. So to check a file's integrity or determining the bpms would be good functions for a tool.
Also, searching for covers from external sources would be a worthwhile application of a tool
To treat the tag data, MP3tag has a lot of functions that also can be called in many cases by using Actions (quick) or incorporating one or more in an action group.
The problems that you describe like
sound to me like a strange approach: the ID3 standard is mainly for MP3 files, yet the mechanism has been adopted for
The ID3 standard has a number of fixed tag fields but also allows user-defined tag fields.
Any tagging program that adheres to the ID3 standard will not corrupt the audio part by adding tag data and any player adhering to the ID3 standard will neither get upset by the standard tag fields nor by the user-definded fields.
But as you have found out: this is not the case with the radio program and some freeware programs.
Also, they seem to have some self-inflicted limitations like a certain cover size.
For already embedded covers MP3tag offers a number of actions:
So it would not be necessary to call a tool to shrink an embedded image from
to
If I were you I would setup a number of tool calls and action groups to do some kind of delivery check to make sure that the files are OK on arrival.
And on a side note: I did not have the impression that we were discussing actions and tools in general here but very detailed a function to call a specifc type of action automatically.