I am adding your name to the list so that you can/will be able to access the page from here (whenever you want to.)
I would use 'can' or 'will be able to' not 'could'. 'could' is either the past tense form of 'can' or a subjunctive form of the verb. Your sentence is a simple statement of fact, and as such doesn't need a subjunctive, nor is it past tense.
cf: I added your name to the list, so that you could access the page from here.
Future tense is indicated using 'will' or 'shall' or 'going to' not could.
I will go to London tomorrow. FT
I could go to London tomorrow, if .... (depends on other factors, is subjunctive.)
Student or Learner