Is it possible to change the format of a Brood War map to play/open on the original StarCraft game/map editor?

Yes but the terrain has to be one of the sc ones (jungle,badlands,space platform,installation,ashworld) and bw units will be removed.
To convert a map you have to save it in starcraft format using a map editor.

The extension for vanilla starcraft is .scm, so when saving, save it as .scm, if there are any units from Broodwar, the editor with automatically remove them. And as he said, it must be a vanilla tileset.

You could always turn to Farty and ask for insane stuff...

So how would i open the map to save it as .scm?

ScmDraft. Check the Download Database

Any editor really, although if you don't want them deleting units, SCM Draft is the way to go, if the map doesn't open properly, try opening it with OS Map first, then open it.

i got scmdraft and i got the map open but how do i save it as .scm?

open the map, file > save as > scm

it won't let me

It lets me

Actually, without deleting broodwar units and still using broodwar terrain, you can open a broodwar map on regular sc. All you need is the BrooDat.mpq. On my laptop, I make maps, but I don't have starcraft on it, I just copied the needed mpqs and moved them to my computer. I put them in the same folder as scmdraft.

i don't have the broodwar expansion so i can't really do much with it, that's why i wanan try and convert a broodwar RP into a starcraft map cause RPs in the original are kinda rare

Use starforge.

StarForge doesn't load up, keeps saying 'error 53 file not found' and then StarForge opens with a blank screen
starting to think it would be easier to create my own RP lol

That's because it's protected.

Use the program I posted to open it up and then resave it.

You could also post the map and I'd be happy to do it for you.

it's not the map which won;t load up it's StarForge itself
and any RP in general i'm looking for really but the Josrestal RP in the staredit database looks cool

When you Save As, [filename].scm instead of [filename].scx

However, being that these are BroodWar RPGs you want to play in Vanilla SC, I'd imagine even if you load up a game on the map, it won't play correctly, with triggers calling for units that don't exist.

Personally, I'd just buy Brood War.

i guess it would be easier, but i don't think any shops sell it anymore, and i've never liked buying online