I have found a solution.
In file ne.h, after #include <stdbool.h> add extern bool search_term;
in file actions.c, after #include <limits.h> add bool search_term = FALSE;
in file actions.c, after case FINDREGEXP_A: add search_term = TRUE;
in file actions.c, after case EXEC_A: add search_term = FALSE;
in file input.c change if (history_buff->num_lines == 0 || ib.len != last->line_len || strncmp(ib.buf, last->line, last->line_len)) add_to_history(ib.buf);
to if (history_buff->num_lines == 0 || ib.len != last->line_len || strncmp(ib.buf, last->line, last->line_len)) if (search_term == true){add_to_history(ib.buf);search_term = false;};