I am making a druid subclass called Circle of the Dragon, and have decided to make a statblock appear in the actions on the character sheet. However I wanted to level up some values as the character gains levels. 

In the code below, I want the breath weapon to gain d10s and the player levels up. How would I reflect this in the code below?

• <strong>Armor Class:</strong> {{proficiency+13#signed}}
• <strong>Speed:</strong> 40ft., <strong>Fly:</strong> 80ft.
• <strong>Saving Throws:</strong> DEX {{proficiency+1#signed}}, CON {{proficiency+2#signed}}, WIS {{proficiency+2#signed}}
• <strong>Damage Immunities.</strong> determined by your Draconic Form trait.
• <strong>Senses.</strong> darkvision 60 ft., passive Perception {{10+proficiency}}
<strong>Actions</strong>
• <em><strong>Multiattack.</strong></em> The dragon makes two attacks: one with its bite and one with its claws.
• <em><strong>Bite.</strong> Melee Weapon Attack: </em>{{proficiency+4#signed}} to hit, reach 10 ft., one target you can see. <em>Hit:</em> <strong>1d10</strong>{{proficiency#signed}} piercing damage.
• <em><strong>Claws.</strong> Melee Weapon Attack: </em>{{proficiency+4#signed}} to hit, reach 5 ft., one target you can see. <em>Hit:</em> <strong>2d6</strong>{{proficiency#signed}} slashing damage.
• <em><strong>Tail.</strong> Melee Weapon Attack: </em>{{proficiency+4#signed}} to hit, reach 15 ft., one target you can see. <em>Hit:</em> <strong>1d8</strong>{{proficiency#signed}} bludgeoning damage. If the target is a creature, it must succeed on a <em>Strength saving throw</em> <strong>({{proficiency+10#signed}})</strong> or be knocked prone.
• <em><strong>Breath Weapon. (Recharge 5-6)</strong> Ranged Attack: </em> reach 30 ft. line, 5 ft. wide <em>Dexterity saving throw</em> <strong>({{proficiency+10#signed}})</strong> On a failed save, the creature takes <strong>2d10</strong> damage of the type determined by your Draconic Form. On a successful save, it takes half as much damage.

<strong>Hit Points:</strong>

Those are made using snippet codes, with a list of what is available here: https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/25930-using-snippet-codes-in-your-homebrew

I don't think it supports a variable number of dice however.

Quote from Houligan >>

I don't think it supports a variable number of dice however.

It's possible with some complex calculations or even better by using a subclass's Level Scaling section and {{scalevalue}}

My concern with OP is all the different #signed snippets used. If a value doesn't need a + or -, then I'd suggest not using #signed at all. Plus there's 13 different snippet codes in that text. Be careful with so many codes in one snippet box as I found 20 pretty much freezes your character sheet.

I have since learned that this was too many snippets and have cut many of them back. I also have removed many of the #signed! Thank you for the help!

When I was testing the stuff in this, I had 2 custom actions. One tested out all the even numbers and the other had all the odd ones. Even at 10 snippet codes each, it still took my character page a moment of two longer than normal to load.

I would suggest people avoid putting 10 or more snippet codes in any one snippet box. Somewhere between 10 and 20 codes and your character sheet may become unresponsive.