Your biggest problem is going to be that Access is not a word processor like Word is. Strikethrough isn't going to be possible unless you have a FONT that already includes a strikethrough because Access doesn't have the direct ability to supply supplemental attributes in a single field.
Stated another way, you don't ask Word to do a relational join directly when doing a Mailmerge. Instead, you write an Access query and then do the merge on the query. Similarly, don't expect to define a word processing function and then implement it in something that isn't a word processor.
You could try something kinky like, if the text box is short enough, optionally superimpose a line on the textbox and control it separately when you want a strikethrough to show. Access could correctly print this, but you still won't be able to save a document containing the line. We are also probably talking about some VBA code to control that line based on some condition you would define.
When you try to save to Word for an Access report with lines, the lines vanish. Which occurs because Access is too stupid to save to Word format, but it can manage Wordpad (.rtf) format. Unfortunately, Wordpad does not know what to do with lines other than eat them.