Here is a complete macro.  It is written in Python, so use APSO to add the code.
Then for convenience, go to Tools → Customize and set a hotkey to run it.
import re
import uno
import unohelper
from com.sun.star.datatransfer import XTransferable, DataFlavor
def copy_and_replace():
    oDoc = XSCRIPTCONTEXT.getDocument()
    oRange = oDoc.getCurrentSelection()
    oCellTopLeft = oRange.getCellByPosition(0, 0)
    sText = oCellTopLeft.getString()
    dReplace = {
        "MS" : "Microsoft",
    }
    pattern = re.compile('|'.join(dReplace.keys()))
    sResult = pattern.sub(lambda x: dReplace[x.group()], sText)
    transferable = Transferable(sResult)
    ctx = XSCRIPTCONTEXT.getComponentContext()
    oClip = ctx.getServiceManager().createInstanceWithContext(
        "com.sun.star.datatransfer.clipboard.SystemClipboard", ctx)
    oClip.setContents(transferable, None)
class Transferable(unohelper.Base, XTransferable):
    """Keep clipboard data and provide them."""
  
    def __init__(self, text):
        df = DataFlavor()
        df.MimeType = "text/plain;charset=utf-16"
        df.HumanPresentableName = "encoded text utf-16"
        self.flavors = [df]
        self.data = [text] #[text.encode('ascii')]
  
    def getTransferData(self, flavor):
        if not flavor: return
        mtype = flavor.MimeType
        for i,f in enumerate(self.flavors):
            if mtype == f.MimeType:
                return self.data[i]
  
    def getTransferDataFlavors(self):
        return tuple(self.flavors)
  
    def isDataFlavorSupported(self, flavor):
        if not flavor: return False
        mtype = flavor.MimeType
        for f in self.flavors:
            if mtype == f.MimeType:
                return True
        return False
# Functions that can be called from Tools -> Macros -> Run Macro.
g_exportedScripts = copy_and_replace,
For example, if a cell contains “The MS product,” then run the macro and paste into Notepad to produce “The Microsoft product.”
For more string changes, simply add entries to the dReplace dictionary.
Sources: