Show latent parameter changes

select name
,      value
from   v$parameter
where  ismodified != 'FALSE'
/

Show non-default parameters

set pages 999 lines 100
col name format a30
col value format a50
select 	name
,	value
from	v$parameter
where	isdefault = 'FALSE'
and	value is not null
order	by name
/

set pages 999 lines 100
select 	name || '=' || decode(type, 2, '''') || value 
	|| decode(type, 2, '''') parameter
from	v$parameter
where	isdefault = 'FALSE'
and	value is not null
order	by name
/

Reset/Unset a spfile parameter

alter system reset <parameter> scope=spfile sid='*'
/