As Tajsateesh has pointed out, one should not post multiple identical threads. I have merged the threads so that members, including you, can view and respond to the query in one place.
Designation and Establishment Matters
Coming to your query: the designation with which you were appointed is what is to be considered for 'establishment matters' purposes. This means that your salary slip, promotion/incentive letters, memos, etc., will be issued in your name with this designation.
The nature of work may vary from time to time, depending on the exigencies, and this should not affect the designation.
Transfer and Designation
However, since you say you have been TRANSFERRED, is this transfer formal - with a formal transfer order; or were you simply directed to report to the Hardware section? What does the Transfer Letter mention your designation as?
Experience Letter Format
As already mentioned earlier, the situation is flexible for the purpose of an experience letter. The usual format of which can be as follows:
"Mr. ABC joined XYZ Co. as a Software Engineer on [date]. During his tenure, he has worked in the Hardware Division, etc."
Warm regards.