"So" means the situation Macbeth just described. A modern equivalent would be "rather than that", or "instead of that". 50-60 years ago takes us to post-World War II, so there's no problem with using modern English there. Just don't mention the iPhone, OK. ;) PS. Thanks Jura for giving us the context! :)

Hi, it would not make sense as it is Shakesperean English. If you want to write about the past write in the past tense. Have a go and we will help you.

Here is the full text To be thus is nothing, 48 But to be safely thus. Our fears in Banquo 49 Stick deep; and in his royalty of nature 50 Reigns that which would be fear'd. 'Tis much he dares; 51 And, to that dauntless temper of his mind, 52 He hath a wisdom that doth guide his valour 53 To act in safety. There is none but he 54 Whose being I do fear: and, under him, 55 My Genius is rebuked; as, it is said, 56 Mark Antony's was by Caesar. He chid the sisters 57 When first they put the name of king upon me, 58 And bade them speak to him; then prophet-like 59 They hail'd him father to a line of kings: 60 Upon my head they placed a fruitless crown, 61 And put a barren sceptre in my gripe, 62 Thence to be wrench'd with an unlineal hand, 63 No son of mine succeeding. If 't be so, 64 For Banquo's issue have I filed my mind; 65 For them the gracious Duncan have I murder'd; 66 Put rancours in the vessel of my peace 67 Only for them; and mine eternal jewel 68 Given to the common enemy of man, 69 To make them kings, the seed of Banquo kings! 70 Rather than so, come fate into the list, 71 And champion me to the utterance! Who's there?