plotting - Prevent Part[] from trying to extract parts of symbolic expressions

If you have a list, e.g.

{1, 2, 3}

then you can extract the $k$th part using Part (list[[k]]):

In[1]:= {1, 2, 3}[[2]]
Out[1]= 2

The problem is that if you provide a symbolic expression in the place of the list, Part will try to decompose it:

In[1]:= list[[2]]
Part::partd: Part specification list[[2]] is longer than depth of object.
Out[1]= list[[2]]

That is, the issue occurs when the overall expression is evaluated before the value of list is known. For example:

In[1]:= list[[2]] /. list -> {1, 2, 3}
Part::partd: Part specification list[[2]] is longer than depth of object.
Out[1]= 2

Although the final output is correct, this produces an annoying spurious error message.

It's even worse if list is a compound expression, because then Part will decompose it, unexpectedly changing its value. For example,

In[1]:= SinCos[x][[1]] /. SinCos -> (θ \[Function] {Sin@θ, Cos@θ})
Out[1]= x

Wat.

Example

I commonly run into this when plotting one dimension of nested functions and data structures.

Suppose I have a function that generates a list of functions according to some parameters:

functions[x_Real, a_, b_, c_] := {Sin@x, Cos@x, Sin[a*x], Cos[b*x], Sin[c*x]};

Now I want to plot the first, third, and fourth functions in the list of functions with parameters $1,2,3$; in this case, $y = \sin(x), \sin(1 \cdot x), \cos(2 \cdot x)$. The obvious way is:

Plot[functions[x, 1, 2, 3][[#]]& /@ {1,3,4} // Evaluate, {x, 0, 5}]

(The Evaluate is needed to get Plot to treat the values as separate functions, so that they will be styled differently.) And Mathematica will dutifully plot... $y = x, 2, 3$:

{Plot[functions[x,1,2,3][[#]]&/@{1,3,4}//Unevaluated,{x,0,5}],
 Plot[functions[x,1,2,3][[#]]&/@{1,3,4}//Evaluate,{x,0,5}]}

Question

How do I prevent Part[] from trying to decompose symbolic expressions when it is evaluated?

I have a workaround below, but I'm interested in whether there's a better way to do it. Is there a standard built-in function that does what I'm looking for?