It is possible for a player to be shown a second yellow card while being substituted. In fact, there have been several instances where this has happened.
One notable example is from the 1980 FA Cup third round match between Stoke City and Burnley. Denis Smith, who was already on a yellow card, limped off with an injured ankle but lingered on the pitch to waste time. This led to Smith being sent off for time-wasting by referee Kevin McNally.
Another example is from a 2008 Steel City derby match between Sheffield Wednesday and Derby County, although it's unclear if he was officially booked for this infraction in the article as he had already been booked earlier. Jermaine Johnson kicked a water bottle into the stands after being substituted but returned to have a shower before being sent off.
On the international level, Rui Costa was famously sent off for time-wasting while leaving the pitch during Portugal's World Cup qualifier against Germany in 1997. Portugal needed to win the match and were leading 1-0 when Costa left the field before he could be replaced by his substitute, resulting in a goal that allowed Germany to equalize and qualify for the 1998 World Cup.
In yet another instance, Clarence Seedorf was booked twice after refusing to leave the pitch via the nearest exit but instead wanted to walk the entire length of the field. He received his first booking for ignoring the referee's instructions and a second one after he continued on despite being told again to leave immediately.
There have been instances where teams did not qualify for the World Cup due to withdrawals or other issues, with countries like Scotland declining to participate because they finished second in qualifying and Portugal being offered a place but declining.
One notable example is from the 1980 FA Cup third round match between Stoke City and Burnley. Denis Smith, who was already on a yellow card, limped off with an injured ankle but lingered on the pitch to waste time. This led to Smith being sent off for time-wasting by referee Kevin McNally.
Another example is from a 2008 Steel City derby match between Sheffield Wednesday and Derby County, although it's unclear if he was officially booked for this infraction in the article as he had already been booked earlier. Jermaine Johnson kicked a water bottle into the stands after being substituted but returned to have a shower before being sent off.
On the international level, Rui Costa was famously sent off for time-wasting while leaving the pitch during Portugal's World Cup qualifier against Germany in 1997. Portugal needed to win the match and were leading 1-0 when Costa left the field before he could be replaced by his substitute, resulting in a goal that allowed Germany to equalize and qualify for the 1998 World Cup.
In yet another instance, Clarence Seedorf was booked twice after refusing to leave the pitch via the nearest exit but instead wanted to walk the entire length of the field. He received his first booking for ignoring the referee's instructions and a second one after he continued on despite being told again to leave immediately.
There have been instances where teams did not qualify for the World Cup due to withdrawals or other issues, with countries like Scotland declining to participate because they finished second in qualifying and Portugal being offered a place but declining.
I think it's kinda cool that we get to see these situations where players try to waste time and really, they're just showing how much they care about their team! Like, Denis Smith was already hurt, so he was literally limping off the pitch thinking "I can still influence this game!" 
And Jermaine Johnson, oh man, who kicks a water bottle? That's some commitment right there! 
As for Clarence Seedorf, dude just wouldn't let go of his time in the spotlight 
. It's funny that it happens with different teams and players too, like Rui Costa trying to be all heroic and then Germany scores and Portugal almost misses out on a spot at the World Cup 
. But you know what? These situations just show us that football is full of drama and passion! 
but hey at least we've got some crazy examples from the past that show us what can happen when players don't follow the rules 
like rui costa, man... did he really have to leave the pitch before his sub could come on? 
. First off, how do refs even know about time-wasting when some players are literally limping around on the field? And what's with these guys who refuse to leave the pitch? It's like they're trying to make a statement or something... Clarence Seedorf, man, that guy was like a rockstar, always causing drama 
. But seriously, have you noticed how often this happens in high-stakes games? It's like players are trying to psych out the refs or the other team. And don't even get me started on that Portugal vs Germany match... what if Costa just wanted to make sure his country got into the World Cup for real? 
The system is clearly rigged, folks 
.
just imagine bein on that pitch, tryin to waste time, gettin another card, and then BOOM outta there! 
also why do ppl try to waste time like dat? is it just frustration or somethin' else? 
anyway back to soccer rules 
i think its kinda lame that teams dont get punished more for wasting time u mean like if ur team is down by 2 goals and ur player is just standing there not even trying anymore thats just frustrating 