Normally you cannot EDIT TMS RFC definitions which defined under transaction code SM59,  but if you want to open these definitions for editing then you can use the following tip…

Go to SM59

Double Click or press the Change button for the TMS RFC defination

Defination will be open but as you can see there is no editing chance for it

Write the word “TOGL” to transaction area and ENTER

Editing will be open after the process like shown below….

Now you can change anything on defination you want…