^
I've found myself stuck in this exact same mess more times than I care to admit—trying to pull CSV files into Excel when the database is using American number formatting.
Like Jack Hayes mentioned, when you're importing (you go to the "Data" tab, then under "Get External data" -> From Text), you can actually specify the data type for each column. My trick is to set any columns containing numbers to text format right away.
After that, you just run a Find / Replace. You’ve got the "Replace All" button right there, so you don't have to waste your life doing individual replacements; it swaps everything in the document in one single click.
Now, if you're dealing with decimals, you absolutely have to use a placeholder—some third, random character during the replace process. I personally always use the @ symbol because I know for a fact it won't show up anywhere else in my data.
For instance, if you have a number like 5,258.56 that needs to become 5.258,56, you can't just swap the comma for a period. If you do that, you'll end up with 5.258.56 and completely screw up the value.
So, here is the workflow: first, replace the comma with @ (leaving you with
5@258.56), then replace the period with a comma (giving you 5@258,56), and finally, replace that @ with a period (to get 5.258,56).
I'm telling you, just use "Replace All" and the whole thing is sorted in a few clicks.
If you're only dealing with integers—just plain old whole numbers—and you simply want to strip out the period, just put the period in the "Find" box, leave the "Replace" box empty, and hit "Replace All." The periods will vanish.🙂
Once that's done, just highlight the columns you need and set the formatting to number.