You won't be able to delete the asterisks with a text editor, because the asterisks in the attached file are not made with text. (Well, technically you could, but we'd have to do some detective work to figure out which text to delete.) They are made of 3 short black lines, and 1 blue line. In some places, the 4 short lines are in a Group, but other times they are part of a much larger group, but not separately grouped.
I'm trying to think of something that sets them apart enough to be able to use Find/Replace. But so far, I can't think of any. Maybe Moini will have an idea?
However, it looks like there are only 7 in this file. Even with having 10 more files, that's still not a ton of work to do it one at a time.
There are a couple of different ways that I would approach it. I'd probably do the first one below.
1 - There's an extension called Deep Ungroup. It will ungroup everything in the file, all at once. And there really are a lot of groups. I can't remember if that extension has been packed with Inkscape now, or if you'll need to install it. But look in Extensions menu > Arrange > Deep Ungroup.
Without that extension, you can still ungroup, but it takes a little more clicking. With the Selection tool, you would use Ctrl + A (or Edit menu > Select All), then click the Ungroup button multiple times, until the status bar says "No groups to ungroup".
After it's all ungrouped, you can use the Selection tool, and drag a little selection box around the 4-line asterisk. That selects all the lines at the same time. Then, just Delete (Delete key or Edit menu > Delete).
If you have the new symbol that you want to use ready, you can paste it in. Oh wait! Forget pasting. There's a nasty bug in Inkscape which only affects Mac users. It will rasterize anything that's pasted. I guess if it doesn't matter if you have raster content in the file, that would work. But if you need all vector content, we'll have to go to "plan b".
2 - (this is not plan b) The 2nd way would be to use Ctrl + click on top of the asterisk. That will select one if the little lines. So you have to do it 4 times for each asterisk. So it's easy to see why I would ungroup, instead of this. But it would be a routine like this: Ctrl + click + delete. And it would be 4 times for each asterisk.
Plan b. Since I'm not a Mac user, I'm not sure how to handle the pasting bug. Normally we suggest using Duplicate instead of Paste. If Inkscape can create the symbol that you want to use, that's fine. Just use Duplicate instead of Copy/Paste. But if you have a symbol that was copied from somewhere else, I don't know how you can get it into the file.
Inkscape has a relatively new Symbols dialog. You can just drag the symbol from the dialog and drop it where you want it. I do wonder whether drag and drop is similar to copy and paste though. Well, just let us know if you run into trouble. We'll try to find plan b
