Can we replace “+” with something else?

You should be able to do that with some simple CSS:

.c-accordion__title:after {
    content: "(Click to Expand)";
}

.is-open > .c-accordion__title:after {
    content: "(Click to Hide)";
}

@antonyalston I replace the +/- with disclosure triangles on the left. Here is the CSS with some other customizing. You can see how it looks here.

/* 
 * Put disclosure triangles before the accordion item title
 * ( +/- occurs on right margin of page already), with a right margin
 */
.c-accordion__title::before {
    position: relative;
    top: 50%;
    right: 0;
    content: "\25B6";
    color: #777;
    -webkit-transform: translateY(-50%);
    transform: translateY(-50%);
    margin-right: 1em;
}

/* Downward disclosure triangle when open */
.is-open .c-accordion__title::before {
    content: "\25BC";
}

/* Remove +/- on the right */
.c-accordion__title::after,
.is-open .c-accordion__title::after {
    content: "";
}

/* Shade the title line; adjust title text */
.c-accordion__title {
    background-color: #f2f2f2;
    padding: 0.2em;
    font-size: 23px;
    font-weight: 400;
}

/* Change shade on hover */
.c-accordion__title:hover {
    background-color: #e0e0ff;
}

/* Indent the content beneath title */
.c-accordion__content {
    margin-left: 2em;
}