First of all, You don't need to change the file extension. Right click on the *.api file and then use open, wins will ask You what to do - choose select a program from the list and choose Notepad.exe.
Secondly- I don't bielieve the EOD has the capability of opening the *.api, so
this is not a solution for You.
If Your *.api cannot be selected in any scenery design tool or won't show up in the screen(Airport for windows, FSSC) check the begining of the code for this lines:
;MACRODESC "some text that describes the macro"
;DEFAULTSCALE 0.10
;DEFAULTPARAMS "definition of textures here", , , , , , , ,
;PARAMDESCR Wall texture, Outer front-back wall tex, Inner front-back wall tex, , , , , , , ,
;DEFAULTRANGE 3000
;DEFAULTDENSITY VERY SPARSE
;TEXTURES "another definition of textures here"
;DESIGNSHAPELINES -120, -100, -120, 100, -120, 100, 120, 100, 120, 100, 120, -100, 120, -100, -120, -100,
;=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
;VODDATA Latitude Longitude Range Scale Rotation Wall_texture Outer_front_texture Inner_front_texture Not_used Visibility Altitude Scenery_complexity(0-5) Not_used Not_used
Hope this helps . . .