I also think Org-mode table src block content to override file is dangerous.
I have another idea. Append src block content to end of file.
I have a sceniro:
```
* SSH config 1
#+BEGIN_SRC conf :tangle "~/.ssh/config"
fragment 1
#+END_SRC
```
```
* SSH config 2
#+BEGIN_SRC conf :tangle "~/.ssh/config"
fragment 2
#+END_SRC
```
When the tangle src blocks are in separate files, this override file way is not suitable.
Of course I can put those src blcoks together, but when I have to organize literate programming files in separately, the override way is not suitable anymore. So hope Org-mode can provide `append` way with an `defcustom` option.