I'm not sure if that's even the right question to ask. I'm very new to this. Basically, what I'm trying to make is the statement
[Firstpassagelink]

[Secondpassagelink]

[Firstpassagelink]:
@set x = 1
{if x=1:a}{if y=1:{@inc x}}{if x=2:b}

[Secondpassagelink]:
@set y = 1
{if y=1:c}{if x=1:{@inc y}}{if y=2:d}

Is something like possible? Can I adjust the value of an attribute based on whether or not the reader clicked a prior link?

You could use the seen command (if you are only doing this section once per game). It would work like this. I put some math-y things in there so you can run formulas.

[[start]]:

@set x=1
@set y=1

[first_passage]

[second_passage]

[first_passage]:

{if seen second_passage:{@x=2}}

x={x}<br>
y={y}

[second_passage]:

{if seen first_passage:{@y=2}}

x={x}<br>
y={y}

Is this what you're looking for?