Can "for" substitute for "due to"?

Yes, you can.

You can but it's more clear as it is, with "due to". If you use "for" there's a slight ambiguity.

Here's an example:

1. But Lim said that they have declined to make an offer for the new contract.

2. But Lim said that they have declined to make an offer for personal reasons.

Someone might think that "personal reasons" themselves were being offered. The ambiguity is removed if the sentence is changed this way:

3. But, due to personal reasons, Lim said that they have declined to make an offer.

4. But, for personal reasons, Lim said that they have declined to make an offer.

How about "because of"... No ambiguity there.

Or, change the order of words:

"But due to personal reasons, Lim said that they have declined to make an offer."

But Lim said that they have declined to make an offer due to personal reasons.

Is "due to personal reasons" redundant?
Can "due to" be used with reason?

"due to personal reasons" is redundant if the reasons why he's declining are irrelevant; however, if it's a causation of declining, it may be relevant.

He would have made an offer but due to him recently losing both arms in an accident, he is declining at present.

He declined to make an offer because (due to the fact that) he just discovered his wife was cheating on him and now doesn't know if he still wants to buy the house.