MySQL 8.0

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version()
8.0.30

with RECURSIVE
  t1(in_text_search) as (
    values
      row('(word1 OR word2) and .net AND (word3 AND word4 AND word5) OR word6 NOT word7')
  ),
  r as (
    select
      0 as occ,
      cast('' as char(127)) as tok,
      in_text_search,
      0 as parentheses,
      cast('process' as char(30)) as status
    from t1
    union all
    select
      r.occ+1,
      case
        when t.tok = 'AND' then '+'
        when t.tok = 'NOT' then '-'
        when t.tok = 'OR' then ' '
        else coalesce(t.tok, '')
      end,
      r.in_text_search,
      p.parentheses,
      case
        when p.parentheses < 0 then 'imbalanced parentheses'
        when t.tok is null then
          case
            when p.parentheses != 0 then 'imbalanced parentheses'
            else 'done'
          end
        else 'process'
      end
    from r,
    LATERAL(
      select
        ucase(regexp_substr(
          r.in_text_search,
          '[()]|[^()[:space:]]+',
          1,
          r.occ+1
        )) as tok
    ) as t,
    LATERAL(
      select
        r.parentheses +
          case
            when t.tok like '(' then 1
            when t.tok like ')' then -1
            else 0
          end as parentheses
    ) as p
    where status = 'process'
  ),
  t2 as (
    select
      occ,
      tok,
      lead(tok, 2) over(order by occ) as tok_2nd,
      status
    from r
  ),
  t3 as (
    select
      occ,
      case
        when tok = '(' and tok_2nd in ('+', '-') then concat(tok, tok_2nd)
        when tok in ('+', '-') then concat(' ', tok)
        else tok
      end as tok,
      status
    from t2
  )
select
  GROUP_CONCAT(tok order by occ separator '') as text_reformatted
from t3
;

text_reformatted
(WORD1 WORD2) +.NET +(+WORD3 +WORD4 +WORD5) WORD6 -WORD7